diff --git a/src/__tests__/unit/file-tree-dnd.test.ts b/src/__tests__/unit/file-tree-dnd.test.ts
new file mode 100644
index 00000000..78dfa63b
--- /dev/null
+++ b/src/__tests__/unit/file-tree-dnd.test.ts
@@ -0,0 +1,87 @@
+import { describe, it } from 'node:test';
+import assert from 'node:assert/strict';
+
+import {
+  appendPathMention,
+  FILE_TREE_DRAG_FALLBACK_MIME,
+  FILE_TREE_DRAG_MIME,
+  hasFileTreeDragType,
+  parseFileTreeDragPayload,
+  readFileTreeDragPayload,
+  serializeFileTreeDragPayload,
+} from '../../lib/file-tree-dnd';
+
+describe('file-tree drag payload helpers', () => {
+  const makeTypes = (...types: string[]) => types as unknown as readonly string[];
+
+  it('serializes and parses file payload', () => {
+    const raw = serializeFileTreeDragPayload({
+      path: 'src/app/page.tsx',
+      name: 'page.tsx',
+      type: 'file',
+    });
+
+    assert.deepEqual(parseFileTreeDragPayload(raw), {
+      path: 'src/app/page.tsx',
+      name: 'page.tsx',
+      type: 'file',
+    });
+  });
+
+  it('normalizes unknown type to file', () => {
+    assert.deepEqual(
+      parseFileTreeDragPayload('{"path":"src","name":"src","type":"weird"}'),
+      { path: 'src', name: 'src', type: 'file' },
+    );
+  });
+
+  it('rejects invalid payloads', () => {
+    assert.equal(parseFileTreeDragPayload(''), null);
+    assert.equal(parseFileTreeDragPayload('not-json'), null);
+    assert.equal(parseFileTreeDragPayload('{"name":"src"}'), null);
+  });
+
+  it('detects supported drag MIME types', () => {
+    assert.equal(hasFileTreeDragType({ types: makeTypes(FILE_TREE_DRAG_MIME) }), true);
+    assert.equal(hasFileTreeDragType({ types: makeTypes(FILE_TREE_DRAG_FALLBACK_MIME) }), true);
+    assert.equal(hasFileTreeDragType({ types: makeTypes('text/plain') }), false);
+  });
+
+  it('reads payload from preferred MIME first', () => {
+    const payload = readFileTreeDragPayload({
+      types: makeTypes(FILE_TREE_DRAG_MIME, FILE_TREE_DRAG_FALLBACK_MIME),
+      getData(type: string) {
+        if (type === FILE_TREE_DRAG_MIME) {
+          return '{"path":"src/components","name":"components","type":"directory"}';
+        }
+        return '';
+      },
+    });
+
+    assert.deepEqual(payload, {
+      path: 'src/components',
+      name: 'components',
+      type: 'directory',
+    });
+  });
+});
+
+describe('appendPathMention', () => {
+  it('appends mention with trailing space', () => {
+    assert.equal(appendPathMention('', 'src/app/page.tsx'), '@src/app/page.tsx ');
+  });
+
+  it('inserts spacing between existing text and mention', () => {
+    assert.equal(
+      appendPathMention('请看这个', 'src/app/page.tsx'),
+      '请看这个 @src/app/page.tsx ',
+    );
+  });
+
+  it('does not duplicate an existing mention', () => {
+    assert.equal(
+      appendPathMention('请看 @src/app/page.tsx ', 'src/app/page.tsx'),
+      '请看 @src/app/page.tsx ',
+    );
+  });
+});
diff --git a/src/components/ai-elements/file-tree.tsx b/src/components/ai-elements/file-tree.tsx
index c7322c45..a6df5392 100644
--- a/src/components/ai-elements/file-tree.tsx
+++ b/src/components/ai-elements/file-tree.tsx
@@ -22,6 +22,11 @@ import {
   useMemo,
   useState,
 } from "react";
+import {
+  FILE_TREE_DRAG_FALLBACK_MIME,
+  FILE_TREE_DRAG_MIME,
+  serializeFileTreeDragPayload,
+} from "@/lib/file-tree-dnd";
 
 interface FileTreeContextType {
   expandedPaths: Set<string>;
@@ -131,6 +136,17 @@ export const FileTreeFolder = ({
     togglePath(path);
   }, [togglePath, path]);
 
+  const handleDragStart = useCallback(
+    (e: React.DragEvent<HTMLDivElement>) => {
+      const payload = serializeFileTreeDragPayload({ path, name, type: "directory" });
+      e.dataTransfer.setData(FILE_TREE_DRAG_MIME, payload);
+      e.dataTransfer.setData(FILE_TREE_DRAG_FALLBACK_MIME, payload);
+      e.dataTransfer.setData("text/plain", path);
+      e.dataTransfer.effectAllowed = "copy";
+    },
+    [name, path]
+  );
+
   const folderContextValue = useMemo(
     () => ({ isExpanded, name, path }),
     [isExpanded, name, path]
@@ -147,6 +163,8 @@ export const FileTreeFolder = ({
           <CollapsibleTrigger asChild>
             <div
               className="flex w-full cursor-pointer items-center gap-1 rounded px-2 py-1 text-left transition-colors hover:bg-muted/50"
+              draggable
+              onDragStart={handleDragStart}
               role="button"
               tabIndex={0}
               onKeyDown={(e) => {
@@ -232,6 +250,17 @@ export const FileTreeFile = ({
     [onAdd, path]
   );
 
+  const handleDragStart = useCallback(
+    (e: React.DragEvent<HTMLDivElement>) => {
+      const payload = serializeFileTreeDragPayload({ path, name, type: "file" });
+      e.dataTransfer.setData(FILE_TREE_DRAG_MIME, payload);
+      e.dataTransfer.setData(FILE_TREE_DRAG_FALLBACK_MIME, payload);
+      e.dataTransfer.setData("text/plain", path);
+      e.dataTransfer.effectAllowed = "copy";
+    },
+    [name, path]
+  );
+
   const fileContextValue = useMemo(() => ({ name, path }), [name, path]);
 
   return (
@@ -243,7 +272,9 @@ export const FileTreeFile = ({
           className
         )}
         onClick={handleClick}
+        onDragStart={handleDragStart}
         onKeyDown={handleKeyDown}
+        draggable
         role="treeitem"
         tabIndex={0}
         {...props}
diff --git a/src/components/chat/MessageInput.tsx b/src/components/chat/MessageInput.tsx
index f0ed151a..8372331d 100644
--- a/src/components/chat/MessageInput.tsx
+++ b/src/components/chat/MessageInput.tsx
@@ -1,6 +1,6 @@
 'use client';
 
-import { useRef, useState, useCallback, useEffect, type KeyboardEvent, type FormEvent } from 'react';
+import { useRef, useState, useCallback, useEffect, type KeyboardEvent, type FormEvent, type DragEvent as ReactDragEvent } from 'react';
 import { Terminal } from "@/components/ui/icon";
 import { useTranslation } from '@/hooks/useTranslation';
 import type { TranslationKey } from '@/i18n';
@@ -35,6 +35,8 @@ import { useCliToolsFetch } from '@/hooks/useCliToolsFetch';
 import { useSlashCommands } from '@/hooks/useSlashCommands';
 import { resolveKeyAction, cycleIndex, resolveDirectSlash, dispatchBadge, buildCliAppend } from '@/lib/message-input-logic';
 import { QuickActions } from './QuickActions';
+import { appendPathMention, hasFileTreeDragType, readFileTreeDragPayload } from '@/lib/file-tree-dnd';
+import { cn } from '@/lib/utils';
 
 interface MessageInputProps {
   onSend: (content: string, files?: FileAttachment[], systemPromptAppend?: string, displayOverride?: string) => void;
@@ -87,6 +89,7 @@ export function MessageInput({
   const textareaRef = useRef<HTMLTextAreaElement>(null);
   const searchInputRef = useRef<HTMLInputElement>(null);
   const cliSearchRef = useRef<HTMLInputElement>(null);
+  const [isFileTreeDragOver, setIsFileTreeDragOver] = useState(false);
   // Persist draft per session so switching chats doesn't lose typed text.
   const draftKey = `codepilot:draft:${sessionId || 'new'}`;
   const [inputValue, setInputValueRaw] = useState(() => {
@@ -165,21 +168,46 @@ export function MessageInput({
     }
   }, [onAssistantTrigger]);
 
+  const handleInsertPathMention = useCallback((filePath: string) => {
+    if (!filePath) return;
+    setInputValue((prev) => appendPathMention(prev, filePath));
+    setTimeout(() => textareaRef.current?.focus(), 0);
+  }, [setInputValue]);
+
   // Listen for file tree "+" button: insert @filepath into textarea
   useEffect(() => {
     const handler = (e: Event) => {
       const filePath = (e as CustomEvent<{ path: string }>).detail?.path;
-      if (!filePath) return;
-      const mention = `@${filePath} `;
-      setInputValue((prev) => {
-        const needsSpace = prev.length > 0 && !prev.endsWith(' ') && !prev.endsWith('\n');
-        return prev + (needsSpace ? ' ' : '') + mention;
-      });
-      setTimeout(() => textareaRef.current?.focus(), 0);
+      handleInsertPathMention(filePath);
     };
     window.addEventListener('insert-file-mention', handler);
     return () => window.removeEventListener('insert-file-mention', handler);
-  }, [setInputValue]);
+  }, [handleInsertPathMention]);
+
+  const handleFileTreeDragOver = useCallback((e: ReactDragEvent<HTMLDivElement>) => {
+    if (!hasFileTreeDragType(e.dataTransfer)) return;
+    e.preventDefault();
+    e.dataTransfer.dropEffect = 'copy';
+    setIsFileTreeDragOver(true);
+  }, []);
+
+  const handleFileTreeDragLeave = useCallback((e: ReactDragEvent<HTMLDivElement>) => {
+    if (e.currentTarget.contains(e.relatedTarget as Node | null)) return;
+    setIsFileTreeDragOver(false);
+  }, []);
+
+  const handleFileTreeDrop = useCallback((e: ReactDragEvent<HTMLDivElement>) => {
+    const payload = readFileTreeDragPayload(e.dataTransfer);
+    if (!payload) return;
+
+    e.preventDefault();
+    setIsFileTreeDragOver(false);
+    handleInsertPathMention(payload.path);
+
+    if (payload.type === 'file') {
+      window.dispatchEvent(new CustomEvent('attach-file-to-chat', { detail: { path: payload.path } }));
+    }
+  }, [handleInsertPathMention]);
 
   const handleSubmit = useCallback(async (msg: { text: string; files: Array<{ type: string; url: string; filename?: string; mediaType?: string }> }, e: FormEvent<HTMLFormElement>) => {
     e.preventDefault();
@@ -367,7 +395,15 @@ export function MessageInput({
   return (
     <div className="bg-background/80 backdrop-blur-lg px-4 pt-2 pb-1">
       <div className="mx-auto">
-        <div className="relative">
+        <div
+          className={cn(
+            "relative",
+            isFileTreeDragOver && "rounded-xl ring-2 ring-primary/40 ring-offset-2 ring-offset-background",
+          )}
+          onDragLeave={handleFileTreeDragLeave}
+          onDragOver={handleFileTreeDragOver}
+          onDrop={handleFileTreeDrop}
+        >
           {/* Slash Command / File Popover */}
           <SlashCommandPopover
             popoverMode={popover.popoverMode}
diff --git a/src/lib/file-tree-dnd.ts b/src/lib/file-tree-dnd.ts
new file mode 100644
index 00000000..fb9fd887
--- /dev/null
+++ b/src/lib/file-tree-dnd.ts
@@ -0,0 +1,58 @@
+export const FILE_TREE_DRAG_MIME = 'application/x-codepilot-path';
+export const FILE_TREE_DRAG_FALLBACK_MIME = 'text/x-codepilot-path';
+
+export type FileTreeDragPayload = {
+  path: string;
+  name: string;
+  type: 'file' | 'directory';
+};
+
+export function serializeFileTreeDragPayload(payload: FileTreeDragPayload): string {
+  return JSON.stringify(payload);
+}
+
+export function parseFileTreeDragPayload(raw: string | null | undefined): FileTreeDragPayload | null {
+  if (!raw) return null;
+
+  try {
+    const parsed = JSON.parse(raw) as Partial<FileTreeDragPayload>;
+    if (!parsed.path || typeof parsed.path !== 'string') return null;
+
+    return {
+      path: parsed.path,
+      name: typeof parsed.name === 'string' ? parsed.name : '',
+      type: parsed.type === 'directory' ? 'directory' : 'file',
+    };
+  } catch {
+    return null;
+  }
+}
+
+export function hasFileTreeDragType(
+  dataTransfer: Pick<DataTransfer, 'types'> | null | undefined,
+): boolean {
+  if (!dataTransfer) return false;
+
+  const types = Array.from(dataTransfer.types as ArrayLike<string>);
+  return types.includes(FILE_TREE_DRAG_MIME) || types.includes(FILE_TREE_DRAG_FALLBACK_MIME);
+}
+
+export function readFileTreeDragPayload(
+  dataTransfer: Pick<DataTransfer, 'getData' | 'types'> | null | undefined,
+): FileTreeDragPayload | null {
+  if (!dataTransfer) return null;
+  if (!hasFileTreeDragType(dataTransfer)) return null;
+
+  return parseFileTreeDragPayload(
+    dataTransfer.getData(FILE_TREE_DRAG_MIME)
+    || dataTransfer.getData(FILE_TREE_DRAG_FALLBACK_MIME),
+  );
+}
+
+export function appendPathMention(inputValue: string, path: string): string {
+  const mention = `@${path}`;
+  if (inputValue.includes(mention)) return inputValue;
+
+  const needsSpace = inputValue.length > 0 && !inputValue.endsWith(' ') && !inputValue.endsWith('\n');
+  return `${inputValue}${needsSpace ? ' ' : ''}${mention} `;
+}