diff --git a/packages/core/src/ide/ide-client.test.ts b/packages/core/src/ide/ide-client.test.ts
index 6955e495..f061156d 100644
--- a/packages/core/src/ide/ide-client.test.ts
+++ b/packages/core/src/ide/ide-client.test.ts
@@ -5,6 +5,7 @@
  */
 
 import { describe, it, expect } from 'vitest';
+import * as path from 'path';
 import { IdeClient } from './ide-client.js';
 
 describe('IdeClient.validateWorkspacePath', () => {
@@ -49,7 +50,7 @@ describe('IdeClient.validateWorkspacePath', () => {
 
   it('should handle multiple workspace paths and return valid', () => {
     const result = IdeClient.validateWorkspacePath(
-      '/some/other/path:/Users/person/gemini-cli',
+      ['/some/other/path', '/Users/person/gemini-cli'].join(path.delimiter),
       'VS Code',
       '/Users/person/gemini-cli/sub-dir',
     );
@@ -58,11 +59,20 @@ describe('IdeClient.validateWorkspacePath', () => {
 
   it('should return invalid if cwd is not in any of the multiple workspace paths', () => {
     const result = IdeClient.validateWorkspacePath(
-      '/some/other/path:/another/path',
+      ['/some/other/path', '/another/path'].join(path.delimiter),
       'VS Code',
       '/Users/person/gemini-cli/sub-dir',
     );
     expect(result.isValid).toBe(false);
     expect(result.error).toContain('Directory mismatch');
   });
+
+  it.skipIf(process.platform !== 'win32')('should handle windows paths', () => {
+    const result = IdeClient.validateWorkspacePath(
+      'c:/some/other/path;d:/Users/person/gemini-cli',
+      'VS Code',
+      'd:/Users/person/gemini-cli/sub-dir',
+    );
+    expect(result.isValid).toBe(true);
+  });
 });
diff --git a/packages/core/src/ide/ide-client.ts b/packages/core/src/ide/ide-client.ts
index 5ec0bb5c..f8ba6ef5 100644
--- a/packages/core/src/ide/ide-client.ts
+++ b/packages/core/src/ide/ide-client.ts
@@ -272,7 +272,7 @@ export class IdeClient {
       };
     }
 
-    const ideWorkspacePaths = ideWorkspacePath.split(':');
+    const ideWorkspacePaths = ideWorkspacePath.split(path.delimiter);
     const realCwd = getRealPath(cwd);
     const isWithinWorkspace = ideWorkspacePaths.some((workspacePath) => {
       const idePath = getRealPath(workspacePath);
diff --git a/packages/vscode-ide-companion/src/extension-multi-folder.test.ts b/packages/vscode-ide-companion/src/extension-multi-folder.test.ts
index bba6ea99..c8fff810 100644
--- a/packages/vscode-ide-companion/src/extension-multi-folder.test.ts
+++ b/packages/vscode-ide-companion/src/extension-multi-folder.test.ts
@@ -6,6 +6,7 @@
 
 import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest';
 import * as vscode from 'vscode';
+import * as path from 'path';
 import { activate } from './extension.js';
 
 vi.mock('vscode', () => ({
@@ -102,7 +103,7 @@ describe('activate with multiple folders', () => {
     );
   });
 
-  it('should set multiple folder paths, separated by a colon', async () => {
+  it('should set multiple folder paths, separated by OS-specific path delimiter', async () => {
     const workspaceFoldersSpy = vi.spyOn(
       vscode.workspace,
       'workspaceFolders',
@@ -117,7 +118,7 @@ describe('activate with multiple folders', () => {
 
     expect(context.environmentVariableCollection.replace).toHaveBeenCalledWith(
       'GEMINI_CLI_IDE_WORKSPACE_PATH',
-      '/foo/bar:/baz/qux',
+      ['/foo/bar', '/baz/qux'].join(path.delimiter),
     );
   });
 
@@ -166,7 +167,7 @@ describe('activate with multiple folders', () => {
 
     expect(context.environmentVariableCollection.replace).toHaveBeenCalledWith(
       'GEMINI_CLI_IDE_WORKSPACE_PATH',
-      '/foo/bar:/baz/qux',
+      ['/foo/bar', '/baz/qux'].join(path.delimiter),
     );
 
     // Simulate removing a folder
@@ -183,4 +184,28 @@ describe('activate with multiple folders', () => {
       '/baz/qux',
     );
   });
+
+  it.skipIf(process.platform !== 'win32')(
+    'should handle windows paths',
+    async () => {
+      const workspaceFoldersSpy = vi.spyOn(
+        vscode.workspace,
+        'workspaceFolders',
+        'get',
+      );
+      workspaceFoldersSpy.mockReturnValue([
+        { uri: { fsPath: 'c:/foo/bar' } },
+        { uri: { fsPath: 'd:/baz/qux' } },
+      ] as vscode.WorkspaceFolder[]);
+
+      await activate(context);
+
+      expect(
+        context.environmentVariableCollection.replace,
+      ).toHaveBeenCalledWith(
+        'GEMINI_CLI_IDE_WORKSPACE_PATH',
+        'c:/foo/bar;d:/baz/qux',
+      );
+    },
+  );
 });
diff --git a/packages/vscode-ide-companion/src/extension.ts b/packages/vscode-ide-companion/src/extension.ts
index a491ac41..30bab801 100644
--- a/packages/vscode-ide-companion/src/extension.ts
+++ b/packages/vscode-ide-companion/src/extension.ts
@@ -5,6 +5,7 @@
  */
 
 import * as vscode from 'vscode';
+import * as path from 'path';
 import { IDEServer } from './ide-server.js';
 import { DiffContentProvider, DiffManager } from './diff-manager.js';
 import { createLogger } from './utils/logger.js';
@@ -23,7 +24,7 @@ function updateWorkspacePath(context: vscode.ExtensionContext) {
   if (workspaceFolders && workspaceFolders.length > 0) {
     const workspacePaths = workspaceFolders
       .map((folder) => folder.uri.fsPath)
-      .join(':');
+      .join(path.delimiter);
     context.environmentVariableCollection.replace(
       IDE_WORKSPACE_PATH_ENV_VAR,
       workspacePaths,