diff --git a/packages/bruno-cli/src/runner/interpolate-vars.js b/packages/bruno-cli/src/runner/interpolate-vars.js
index 7f76aab14..fa531082f 100644
--- a/packages/bruno-cli/src/runner/interpolate-vars.js
+++ b/packages/bruno-cli/src/runner/interpolate-vars.js
@@ -102,7 +102,9 @@ const interpolateVars = (request, envVariables = {}, runtimeVariables = {}, proc
         }));
       }
     } else if (contentType.startsWith('multipart/')) {
-      if (Array.isArray(request?.data) && !isFormData(request.data)) {
+      if (request?.data && typeof request.data === 'string') {
+        request.data = _interpolate(request.data);
+      } else if (Array.isArray(request?.data) && !isFormData(request.data)) {
         try {
           request.data = request?.data?.map((d) => ({
             ...d,
diff --git a/packages/bruno-cli/src/runner/run-single-request.js b/packages/bruno-cli/src/runner/run-single-request.js
index 0479ad951..b7f6a3054 100644
--- a/packages/bruno-cli/src/runner/run-single-request.js
+++ b/packages/bruno-cli/src/runner/run-single-request.js
@@ -487,7 +487,7 @@ const runSingleRequest = async function (
 
     const contentType = contentTypeHeader ? request.headers[contentTypeHeader] : '';
     if (typeof contentType === 'string' && contentType.startsWith('multipart/')) {
-      if (!isFormData(request?.data)) {
+      if (typeof request.data !== 'string' && !isFormData(request?.data)) {
         request._originalMultipartData = request.data;
         request.collectionPath = collectionPath;
         let form = createFormData(request.data, collectionPath);
diff --git a/packages/bruno-cli/tests/runner/interpolate-vars.spec.js b/packages/bruno-cli/tests/runner/interpolate-vars.spec.js
index 4f39185c3..ce105c67b 100644
--- a/packages/bruno-cli/tests/runner/interpolate-vars.spec.js
+++ b/packages/bruno-cli/tests/runner/interpolate-vars.spec.js
@@ -18,6 +18,58 @@ describe('interpolate-vars: interpolateVars', () => {
     const result = interpolateVars(request, { shouldNotApply: 'value' }, null, null);
     expect(result.data).toBe(streamPayload);
   });
+
+  it('preserves raw string body when Content-Type is multipart/mixed', () => {
+    const rawMultipartBody = [
+      '--TestBoundary123',
+      'Content-Type: application/json',
+      '',
+      '{"test": true}',
+      '--TestBoundary123--',
+      ''
+    ].join('\r\n');
+
+    const request = {
+      method: 'POST',
+      mode: 'text',
+      url: 'https://httpbin.dev/post',
+      headers: { 'content-type': 'multipart/mixed; boundary=TestBoundary123' },
+      data: rawMultipartBody
+    };
+
+    const result = interpolateVars(request, {}, null, null);
+    expect(result.data).toBe(rawMultipartBody);
+  });
+
+  it('interpolates variables in raw multipart/mixed string body', () => {
+    const boundary = 'CustomBoundary123';
+    const rawMultipartBody = [
+      `--${boundary}`,
+      'Content-Type: text/plain',
+      '',
+      'Token: {{token}}',
+      `--${boundary}`,
+      'Content-Type: application/json',
+      '',
+      '{"id": "{{id}}", "msg": "{{msg}}"}',
+      `--${boundary}--`,
+      ''
+    ].join('\r\n');
+
+    const request = {
+      method: 'POST',
+      mode: 'text',
+      url: 'https://api.example/send',
+      headers: { 'content-type': `multipart/mixed; boundary=${boundary}` },
+      data: rawMultipartBody
+    };
+
+    const result = interpolateVars(request, { token: 'abc123', id: 42, msg: 'hello' }, null, null);
+    expect(result.data).toContain('Token: abc123');
+    expect(result.data).toContain('{"id": "42", "msg": "hello"}');
+    expect(result.data).toContain(`--${boundary}`);
+    expect(result.data).toContain(`--${boundary}--`);
+  });
 });
 
 describe('interpolate-vars: api key header name sidecar', () => {
diff --git a/packages/bruno-electron/src/ipc/network/index.js b/packages/bruno-electron/src/ipc/network/index.js
index 73fbf34d1..ca9a28c55 100644
--- a/packages/bruno-electron/src/ipc/network/index.js
+++ b/packages/bruno-electron/src/ipc/network/index.js
@@ -607,7 +607,7 @@ const registerNetworkIpc = (mainWindow) => {
 
     const contentType = contentTypeHeader ? request.headers[contentTypeHeader] : '';
     if (typeof contentType === 'string' && contentType.startsWith('multipart/')) {
-      if (!isFormData(request.data)) {
+      if (typeof request.data !== 'string' && !isFormData(request.data)) {
         request._originalMultipartData = request.data;
         request.collectionPath = collectionPath;
         let form = createFormData(request.data, collectionPath);
diff --git a/packages/bruno-electron/src/ipc/network/interpolate-vars.js b/packages/bruno-electron/src/ipc/network/interpolate-vars.js
index 81e170e5d..7497926e7 100644
--- a/packages/bruno-electron/src/ipc/network/interpolate-vars.js
+++ b/packages/bruno-electron/src/ipc/network/interpolate-vars.js
@@ -140,7 +140,9 @@ const interpolateVars = (request, envVariables = {}, runtimeVariables = {}, proc
         }));
       }
     } else if (contentType.startsWith('multipart/')) {
-      if (Array.isArray(request?.data) && !isFormData(request.data)) {
+      if (request?.data && typeof request.data === 'string') {
+        request.data = _interpolate(request.data);
+      } else if (Array.isArray(request?.data) && !isFormData(request.data)) {
         try {
           request.data = request?.data?.map((d) => ({
             ...d,
diff --git a/packages/bruno-electron/tests/network/interpolate-vars.spec.js b/packages/bruno-electron/tests/network/interpolate-vars.spec.js
index 48e1a9f9d..9622e8f6d 100644
--- a/packages/bruno-electron/tests/network/interpolate-vars.spec.js
+++ b/packages/bruno-electron/tests/network/interpolate-vars.spec.js
@@ -425,6 +425,200 @@ describe('interpolate-vars: interpolateVars', () => {
       expect(result.data).toContain('{"test": true}');
       expect(result.data).toContain('--TestBoundary123--');
     });
+
+    it('interpolates variables in text-based multipart/mixed body with manual boundaries', () => {
+      // User manually constructs a multipart/mixed body as a string
+      const boundary = 'CustomBoundary123';
+      const rawMultipartBody = [
+        `--${boundary}`,
+        'Content-Type: text/plain',
+        '',
+        'Token: {{token}}',
+        `--${boundary}`,
+        'Content-Type: application/json',
+        '',
+        '{"id": "{{id}}", "msg": "{{msg}}"}',
+        `--${boundary}--`,
+        ''
+      ].join('\r\n');
+
+      const request = {
+        method: 'POST',
+        url: 'https://api.example/send',
+        headers: { 'content-type': `multipart/mixed; boundary=${boundary}` },
+        data: rawMultipartBody
+      };
+
+      const result = interpolateVars(request, { token: 'abc123', id: 42, msg: 'hello' }, null, null);
+
+      expect(result.data).toContain('Token: abc123');
+      expect(result.data).toContain('{"id": "42", "msg": "hello"}');
+      // Ensure boundaries are preserved
+      expect(result.data).toContain(`--${boundary}`);
+      expect(result.data).toContain(`--${boundary}--`);
+    });
+
+    it('interpolates variables in boundary lines themselves', () => {
+      const boundaryVar = 'BoundaryVar';
+      const rawMultipartBody = [
+        `--{{boundary}}`,
+        'Content-Type: text/plain',
+        '',
+        'Hello',
+        `--{{boundary}}--`,
+        ''
+      ].join('\r\n');
+      const request = {
+        method: 'POST',
+        url: 'https://api.example/send',
+        headers: { 'content-type': 'multipart/mixed; boundary={{boundary}}' },
+        data: rawMultipartBody
+      };
+      const result = interpolateVars(request, { boundary: boundaryVar }, null, null);
+      expect(result.data).toContain(`--${boundaryVar}`);
+      expect(result.data).toContain(`--${boundaryVar}--`);
+    });
+
+    it('interpolates variables that resolve to empty string or undefined', () => {
+      const boundary = 'B';
+      const rawMultipartBody = [
+        `--${boundary}`,
+        'Content-Type: text/plain',
+        '',
+        'Token: {{missingVar}}',
+        `--${boundary}--`,
+        ''
+      ].join('\r\n');
+      const request = {
+        method: 'POST',
+        url: 'https://api.example/send',
+        headers: { 'content-type': `multipart/mixed; boundary=${boundary}` },
+        data: rawMultipartBody
+      };
+      const result = interpolateVars(request, {} /* no missingVar */, null, null);
+      expect(result.data).toContain('Token: ');
+    });
+
+    it('interpolates multiple variables in a single line or JSON object', () => {
+      const boundary = 'B2';
+      const rawMultipartBody = [
+        `--${boundary}`,
+        'Content-Type: application/json',
+        '',
+        '{"id": "{{id}}", "msg": "{{msg}}", "extra": "{{extra}}"}',
+        `--${boundary}--`,
+        ''
+      ].join('\r\n');
+      const request = {
+        method: 'POST',
+        url: 'https://api.example/send',
+        headers: { 'content-type': `multipart/mixed; boundary=${boundary}` },
+        data: rawMultipartBody
+      };
+      const result = interpolateVars(request, { id: 1, msg: 'hi', extra: 'x' }, null, null);
+      expect(result.data).toContain('"id": "1", "msg": "hi", "extra": "x"');
+    });
+
+    it('interpolates variables inside quoted and unquoted contexts', () => {
+      const boundary = 'B3';
+      const rawMultipartBody = [
+        `--${boundary}`,
+        'Content-Disposition: form-data; name="{{fieldName}}"',
+        '',
+        'Value',
+        `--${boundary}--`,
+        ''
+      ].join('\r\n');
+      const request = {
+        method: 'POST',
+        url: 'https://api.example/send',
+        headers: { 'content-type': `multipart/mixed; boundary=${boundary}` },
+        data: rawMultipartBody
+      };
+      const result = interpolateVars(request, { fieldName: 'theField' }, null, null);
+      expect(result.data).toContain('name="theField"');
+    });
+
+    it('interpolates variables in both part headers and part bodies', () => {
+      const boundary = 'B4';
+      const rawMultipartBody = [
+        `--${boundary}`,
+        'Content-Type: text/plain; charset={{charset}}',
+        '',
+        'Token: {{token}}',
+        `--${boundary}--`,
+        ''
+      ].join('\r\n');
+      const request = {
+        method: 'POST',
+        url: 'https://api.example/send',
+        headers: { 'content-type': `multipart/mixed; boundary=${boundary}` },
+        data: rawMultipartBody
+      };
+      const result = interpolateVars(request, { charset: 'utf-8', token: 'abc' }, null, null);
+      expect(result.data).toContain('charset=utf-8');
+      expect(result.data).toContain('Token: abc');
+    });
+
+    it('interpolates variables in the final boundary line', () => {
+      const boundary = 'B5';
+      const rawMultipartBody = [
+        `--${boundary}`,
+        'Content-Type: text/plain',
+        '',
+        'End',
+        `--{{finalBoundary}}--`,
+        ''
+      ].join('\r\n');
+      const request = {
+        method: 'POST',
+        url: 'https://api.example/send',
+        headers: { 'content-type': `multipart/mixed; boundary=${boundary}` },
+        data: rawMultipartBody
+      };
+      const result = interpolateVars(request, { finalBoundary: boundary }, null, null);
+      expect(result.data).toContain(`--${boundary}--`);
+    });
+
+    it('interpolates variables that appear multiple times in the body', () => {
+      const boundary = 'B6';
+      const rawMultipartBody = [
+        `--${boundary}`,
+        'Content-Type: text/plain',
+        '',
+        'Token: {{token}}, Again: {{token}}',
+        `--${boundary}--`,
+        ''
+      ].join('\r\n');
+      const request = {
+        method: 'POST',
+        url: 'https://api.example/send',
+        headers: { 'content-type': `multipart/mixed; boundary=${boundary}` },
+        data: rawMultipartBody
+      };
+      const result = interpolateVars(request, { token: 'repeat' }, null, null);
+      expect(result.data.match(/repeat/g).length).toBe(2);
+    });
+
+    it('leaves body unchanged if no variables present', () => {
+      const boundary = 'B7';
+      const rawMultipartBody = [
+        `--${boundary}`,
+        'Content-Type: text/plain',
+        '',
+        'No variables here',
+        `--${boundary}--`,
+        ''
+      ].join('\r\n');
+      const request = {
+        method: 'POST',
+        url: 'https://api.example/send',
+        headers: { 'content-type': `multipart/mixed; boundary=${boundary}` },
+        data: rawMultipartBody
+      };
+      const result = interpolateVars(request, {}, null, null);
+      expect(result.data).toBe(rawMultipartBody);
+    });
   });
 
   describe('File body streaming', () => {
diff --git a/packages/bruno-tests/collection/multipart/content-types-mixed-interpolation.bru b/packages/bruno-tests/collection/multipart/content-types-mixed-interpolation.bru
new file mode 100644
index 000000000..0052b5c62
--- /dev/null
+++ b/packages/bruno-tests/collection/multipart/content-types-mixed-interpolation.bru
@@ -0,0 +1,34 @@
+meta {
+  name: content-types-mixed-interpolation
+  type: http
+  seq: 1
+}
+
+post {
+  url: {{echo-host}}
+  body: text
+  auth: inherit
+}
+
+body:text {
+  ------MyCustomBoundaryString
+  Content-Disposition: form-data; name="metadata"
+  Content-Type: application/json
+  
+  {{version}}
+  
+  ------MyCustomBoundaryString--
+}
+
+vars:pre-request {
+  version: 0.0.1
+}
+
+assert {
+  res.body: contains 0.0.1
+}
+
+settings {
+  encodeUrl: true
+  timeout: 0
+}
diff --git a/packages/bruno-tests/collection/multipart/multipart-mixed-form-data-file.bru b/packages/bruno-tests/collection/multipart/multipart-mixed-form-data-file.bru
new file mode 100644
index 000000000..0da260b05
--- /dev/null
+++ b/packages/bruno-tests/collection/multipart/multipart-mixed-form-data-file.bru
@@ -0,0 +1,20 @@
+meta {
+  name: multipart-mixed-form-data-file
+  type: http
+  seq: 3
+}
+
+post {
+  url: {{echo-host}}
+  body: multipartForm
+  auth: none
+}
+
+body:multipart-form {
+  sample: @file(bruno.png) @contentType(image/png)
+}
+
+assert {
+  res.body: matches ^[-]+[a-z0-9]+
+  res.body: contains Content-Type: image/png
+}
diff --git a/packages/bruno-tests/collection/multipart/multipart-mixed-form-data-parse.bru b/packages/bruno-tests/collection/multipart/multipart-mixed-form-data-parse.bru
new file mode 100644
index 000000000..f25bf3b42
--- /dev/null
+++ b/packages/bruno-tests/collection/multipart/multipart-mixed-form-data-parse.bru
@@ -0,0 +1,23 @@
+meta {
+  name: multipart-mixed-form-data-parse
+  type: http
+  seq: 1
+}
+
+post {
+  url: {{echo-host}}
+  body: multipartForm
+  auth: none
+}
+
+headers {
+  Content-Type: multipart/mixed
+}
+
+body:multipart-form {
+  sample: sample
+}
+
+assert {
+  res.body: matches ^[-]+[a-z0-9]+
+}