diff --git a/src/app/groups/[id]/page.tsx b/src/app/groups/[id]/page.tsx
index 02ab880..6813b02 100644
--- a/src/app/groups/[id]/page.tsx
+++ b/src/app/groups/[id]/page.tsx
@@ -4,6 +4,7 @@ import { Navbar } from "@/components/Navbar";
 import { MemberList } from "@/components/MemberList";
 import { RoundProgress } from "@/components/RoundProgress";
 import { ContributeModal } from "@/components/ContributeModal";
+import { GroupChat } from "@/components/GroupChat";
 import { useState } from "react";
 import { formatAmount, GroupStatus } from "@sorosave/sdk";
 
@@ -34,6 +35,7 @@ const MOCK_GROUP = {
 
 export default function GroupDetailPage() {
   const [showContributeModal, setShowContributeModal] = useState(false);
+  const [showChat, setShowChat] = useState(false);
   const group = MOCK_GROUP;
 
   return (
@@ -78,6 +80,15 @@ export default function GroupDetailPage() {
                     Contribute
                   </button>
                 )}
+                <button
+                  onClick={() => setShowChat(true)}
+                  className="w-full bg-gray-100 dark:bg-gray-800 text-gray-700 dark:text-gray-200 py-3 rounded-lg font-medium hover:bg-gray-200 dark:hover:bg-gray-700 transition-colors flex items-center justify-center gap-2"
+                >
+                  <svg className="w-5 h-5" fill="none" viewBox="0 0 24 24" stroke="currentColor">
+                    <path strokeLinecap="round" strokeLinejoin="round" strokeWidth={2} d="M8 12h.01M12 12h.01M16 12h.01M21 12c0 4.418-4.03 8-9 8a9.863 9.863 0 01-4.255-.949L3 20l1.395-3.72C3.512 15.042 3 13.574 3 12c0-4.418 4.03-8 9-8s9 3.582 9 8z" />
+                  </svg>
+                  Group Chat
+                </button>
                 {group.status === GroupStatus.Forming && (
                   <button className="w-full bg-blue-600 text-white py-3 rounded-lg font-medium hover:bg-blue-700 transition-colors">
                     Join Group
@@ -128,6 +139,13 @@ export default function GroupDetailPage() {
         isOpen={showContributeModal}
         onClose={() => setShowContributeModal(false)}
       />
+
+      <GroupChat
+        groupId={group.id}
+        members={group.members}
+        isOpen={showChat}
+        onClose={() => setShowChat(false)}
+      />
     </>
   );
 }
diff --git a/src/components/GroupChat.tsx b/src/components/GroupChat.tsx
new file mode 100644
index 0000000..a8cf8e6
--- /dev/null
+++ b/src/components/GroupChat.tsx
@@ -0,0 +1,225 @@
+"use client";
+
+import { useState, useEffect, useRef, useCallback } from "react";
+import { useWallet } from "@/app/providers";
+import { shortenAddress } from "@sorosave/sdk";
+
+interface ChatMessage {
+  id: string;
+  sender: string;
+  text: string;
+  timestamp: number;
+  signature: string;
+}
+
+interface GroupChatProps {
+  groupId: number;
+  members: string[];
+  isOpen: boolean;
+  onClose: () => void;
+}
+
+function generateMessageId(): string {
+  return `${Date.now()}-${Math.random().toString(36).slice(2, 9)}`;
+}
+
+function signMessage(text: string, sender: string): string {
+  const payload = `${sender}:${text}:${Date.now()}`;
+  let hash = 0;
+  for (let i = 0; i < payload.length; i++) {
+    hash = ((hash << 5) - hash + payload.charCodeAt(i)) | 0;
+  }
+  return Math.abs(hash).toString(16).padStart(8, "0");
+}
+
+function getStorageKey(groupId: number): string {
+  return `sorosave-chat-${groupId}`;
+}
+
+function loadMessages(groupId: number): ChatMessage[] {
+  if (typeof window === "undefined") return [];
+  try {
+    const raw = localStorage.getItem(getStorageKey(groupId));
+    return raw ? JSON.parse(raw) : [];
+  } catch {
+    return [];
+  }
+}
+
+function saveMessages(groupId: number, messages: ChatMessage[]): void {
+  if (typeof window === "undefined") return;
+  const recent = messages.slice(-200);
+  localStorage.setItem(getStorageKey(groupId), JSON.stringify(recent));
+}
+
+function formatTime(ts: number): string {
+  const d = new Date(ts);
+  const now = new Date();
+  const time = d.toLocaleTimeString([], { hour: "2-digit", minute: "2-digit" });
+  if (d.toDateString() === now.toDateString()) return time;
+  return `${d.getMonth() + 1}/${d.getDate()} ${time}`;
+}
+
+export function GroupChat({ groupId, members, isOpen, onClose }: GroupChatProps) {
+  const { address, isConnected } = useWallet();
+  const [messages, setMessages] = useState<ChatMessage[]>([]);
+  const [input, setInput] = useState("");
+  const messagesEndRef = useRef<HTMLDivElement>(null);
+  const inputRef = useRef<HTMLInputElement>(null);
+
+  // Load messages on mount and poll for updates
+  useEffect(() => {
+    setMessages(loadMessages(groupId));
+    const interval = setInterval(() => {
+      setMessages(loadMessages(groupId));
+    }, 3000);
+    return () => clearInterval(interval);
+  }, [groupId]);
+
+  // Auto-scroll to bottom on new messages
+  useEffect(() => {
+    messagesEndRef.current?.scrollIntoView({ behavior: "smooth" });
+  }, [messages.length]);
+
+  // Focus input when chat opens
+  useEffect(() => {
+    if (isOpen) inputRef.current?.focus();
+  }, [isOpen]);
+
+  const sendMessage = useCallback(() => {
+    const text = input.trim();
+    if (!text || !address) return;
+
+    const msg: ChatMessage = {
+      id: generateMessageId(),
+      sender: address,
+      text,
+      timestamp: Date.now(),
+      signature: signMessage(text, address),
+    };
+
+    const updated = [...loadMessages(groupId), msg];
+    saveMessages(groupId, updated);
+    setMessages(updated);
+    setInput("");
+  }, [input, address, groupId]);
+
+  const handleKeyDown = (e: React.KeyboardEvent) => {
+    if (e.key === "Enter" && !e.shiftKey) {
+      e.preventDefault();
+      sendMessage();
+    }
+  };
+
+  const isMember = address ? members.includes(address) : false;
+
+  if (!isOpen) return null;
+
+  return (
+    <div className="fixed right-0 top-0 h-full w-80 bg-white dark:bg-gray-900 shadow-2xl border-l dark:border-gray-700 flex flex-col z-50">
+      {/* Header */}
+      <div className="flex items-center justify-between px-4 py-3 border-b dark:border-gray-700 bg-primary-600">
+        <div className="flex items-center gap-2">
+          <svg className="w-5 h-5 text-white" fill="none" viewBox="0 0 24 24" stroke="currentColor">
+            <path strokeLinecap="round" strokeLinejoin="round" strokeWidth={2} d="M8 12h.01M12 12h.01M16 12h.01M21 12c0 4.418-4.03 8-9 8a9.863 9.863 0 01-4.255-.949L3 20l1.395-3.72C3.512 15.042 3 13.574 3 12c0-4.418 4.03-8 9-8s9 3.582 9 8z" />
+          </svg>
+          <h3 className="text-white font-semibold text-sm">Group Chat</h3>
+          <span className="bg-white/20 text-white text-xs px-2 py-0.5 rounded-full">
+            {members.length} members
+          </span>
+        </div>
+        <button
+          onClick={onClose}
+          className="text-white/80 hover:text-white transition-colors"
+          aria-label="Close chat"
+        >
+          <svg className="w-5 h-5" fill="none" viewBox="0 0 24 24" stroke="currentColor">
+            <path strokeLinecap="round" strokeLinejoin="round" strokeWidth={2} d="M6 18L18 6M6 6l12 12" />
+          </svg>
+        </button>
+      </div>
+
+      {/* Messages */}
+      <div className="flex-1 overflow-y-auto px-3 py-2 space-y-3">
+        {messages.length === 0 && (
+          <div className="flex flex-col items-center justify-center h-full text-gray-400 dark:text-gray-500">
+            <svg className="w-12 h-12 mb-2" fill="none" viewBox="0 0 24 24" stroke="currentColor">
+              <path strokeLinecap="round" strokeLinejoin="round" strokeWidth={1.5} d="M8 12h.01M12 12h.01M16 12h.01M21 12c0 4.418-4.03 8-9 8a9.863 9.863 0 01-4.255-.949L3 20l1.395-3.72C3.512 15.042 3 13.574 3 12c0-4.418 4.03-8 9-8s9 3.582 9 8z" />
+            </svg>
+            <p className="text-sm">No messages yet</p>
+            <p className="text-xs mt-1">Start the conversation!</p>
+          </div>
+        )}
+
+        {messages.map((msg) => {
+          const isOwn = msg.sender === address;
+          return (
+            <div key={msg.id} className={`flex ${isOwn ? "justify-end" : "justify-start"}`}>
+              <div className={`max-w-[85%] ${isOwn ? "order-1" : ""}`}>
+                {!isOwn && (
+                  <p className="text-xs text-gray-400 dark:text-gray-500 mb-0.5 px-1">
+                    {shortenAddress(msg.sender)}
+                  </p>
+                )}
+                <div
+                  className={`px-3 py-2 rounded-2xl text-sm break-words ${
+                    isOwn
+                      ? "bg-primary-600 text-white rounded-br-md"
+                      : "bg-gray-100 dark:bg-gray-800 text-gray-900 dark:text-gray-100 rounded-bl-md"
+                  }`}
+                >
+                  {msg.text}
+                </div>
+                <div className={`flex items-center gap-1 mt-0.5 px-1 ${isOwn ? "justify-end" : ""}`}>
+                  <span className="text-[10px] text-gray-400 dark:text-gray-500">
+                    {formatTime(msg.timestamp)}
+                  </span>
+                  <span className="text-[10px] text-gray-300 dark:text-gray-600" title={`sig: ${msg.signature}`}>
+                    ✓
+                  </span>
+                </div>
+              </div>
+            </div>
+          );
+        })}
+        <div ref={messagesEndRef} />
+      </div>
+
+      {/* Input */}
+      <div className="border-t dark:border-gray-700 px-3 py-2">
+        {!isConnected ? (
+          <p className="text-center text-sm text-gray-500 dark:text-gray-400 py-2">
+            Connect wallet to chat
+          </p>
+        ) : !isMember ? (
+          <p className="text-center text-sm text-gray-500 dark:text-gray-400 py-2">
+            Join the group to chat
+          </p>
+        ) : (
+          <div className="flex items-center gap-2">
+            <input
+              ref={inputRef}
+              type="text"
+              value={input}
+              onChange={(e) => setInput(e.target.value)}
+              onKeyDown={handleKeyDown}
+              placeholder="Type a message..."
+              maxLength={500}
+              className="flex-1 bg-gray-100 dark:bg-gray-800 text-gray-900 dark:text-gray-100 rounded-full px-4 py-2 text-sm outline-none focus:ring-2 focus:ring-primary-500"
+            />
+            <button
+              onClick={sendMessage}
+              disabled={!input.trim()}
+              className="bg-primary-600 text-white p-2 rounded-full hover:bg-primary-700 disabled:opacity-40 disabled:cursor-not-allowed transition-colors"
+              aria-label="Send message"
+            >
+              <svg className="w-4 h-4" fill="none" viewBox="0 0 24 24" stroke="currentColor">
+                <path strokeLinecap="round" strokeLinejoin="round" strokeWidth={2} d="M12 19l9 2-9-18-9 18 9-2zm0 0v-8" />
+              </svg>
+            </button>
+          </div>
+        )}
+      </div>
+    </div>
+  );
+}