diff --git a/src/components/chat/Chat.tsx b/src/components/chat/Chat.tsx
index 3746eff..0ac4cd9 100644
--- a/src/components/chat/Chat.tsx
+++ b/src/components/chat/Chat.tsx
@@ -1,4 +1,4 @@
-import { useEffect, useState } from 'react';
+import { useState } from 'react';
 
 import ChatButton from '@/components/chat/ChatButton';
 import ChatDetail from '@/components/chat/ChatDetail';
@@ -41,10 +41,11 @@ const Chat = ({
   isUser,
   shopImageUrl,
 }: ChatProps) => {
+  // TODO: 커스텀 훅으로 빼기.
   const seller: SellerInfo = { sellerId: sellerId, shopName: sellerName };
   const product: ProductInfo = { productId: productId, productName: productName };
   const [user, setUser] = useState<UserInfo>({ userId: userId, userName: userName });
-  const [isCustomRoomId, setIsCustomRoomId] = useState<boolean>(true);
+  const [isNowChatRoom, setIsNowChatRoom] = useState<boolean>(false);
 
   const isSeller = isUser;
   const role = isSeller ? 'seller' : 'user';
@@ -65,45 +66,43 @@ const Chat = ({
     return customRoomId;
   }
 
-  /** clickPrevButton() : 채팅방에서 뒤로가기 버튼 누르면
-   * 1. 분기처리를 위해 customRoomId값을 빈 스트링을 넣는다. */
+  /** clickPrevButton() : 채팅방에서 뒤로가기 버튼 */
   const clickPrevButton = () => {
-    setCustomRoomId('');
+    setIsNowChatRoom((prev) => !prev);
   };
 
   /** clickListBox() : 채팅list에서 해당 채팅방으로 들어가기 위해
-   * 1. isCustomRoomId를 false,
+   * 1. isNowChatRoom로 분기처리,
    * 2. ChatBody.tsx에서 custumroomId를 받아와서 ChatList.tsx로 넘겨줌.
    * 3. seller일때 현재 디테일에서 넘어오는 userId, userName값은 판매자의 정보여서 ChatList.tsx에서
         문의한 구매자의 userId값, userName값을 가져옴.
    */
   const clickListBox = (customRoomId: string, userId: number, userName: string) => {
-    setIsCustomRoomId((prev) => !prev);
+    setIsNowChatRoom((prev) => !prev);
     setCustomRoomId(customRoomId);
     setUser({ ...user, userId, userName });
   };
 
   const handleOpen = () => {
     setIsModalOpen((prev) => !prev);
+    setIsNowChatRoom(false);
   };
 
-  useEffect(() => {
-    if (customRoomId.length === 0) {
-      setIsCustomRoomId((prev) => !prev);
-    }
-  }, [customRoomId]);
+  console.log('isNowChatRoom', isNowChatRoom);
 
   return (
     <>
       <ChatButton handleOpen={handleOpen} />
       {isModalOpen && isSeller && (
         <S.Chat>
-          {isCustomRoomId ? (
+          {!isNowChatRoom ? (
             <ChatList
               handleOpen={handleOpen}
               clickListBox={clickListBox}
               seller={seller}
+              user={user}
               isSeller={isSeller}
+              role={role}
               product={product}
             />
           ) : (
@@ -122,12 +121,14 @@ const Chat = ({
       )}
       {isModalOpen && !isSeller && (
         <S.Chat>
-          {!isCustomRoomId ? (
+          {isNowChatRoom ? (
             <ChatList
               handleOpen={handleOpen}
               clickListBox={clickListBox}
               seller={seller}
+              user={user}
               isSeller={isSeller}
+              role={role}
               product={product}
             />
           ) : (
diff --git a/src/components/chat/ChatList.tsx b/src/components/chat/ChatList.tsx
index c3b857c..dc097da 100644
--- a/src/components/chat/ChatList.tsx
+++ b/src/components/chat/ChatList.tsx
@@ -3,7 +3,8 @@ import { useEffect, useState } from 'react';
 import { sellerChatList, userChatList } from '@/apis/chat';
 import ChatBody from '@/components/chat/chatList/ChatBody';
 import ChatHeader from '@/components/chat/chatList/ChatHeader';
-import { Message } from '@/models/chat';
+import { useSSE } from '@/hooks/useSSE';
+import { Message, UserInfo } from '@/models/chat';
 
 export type Chat = {
   [timestamp: string]: Message;
@@ -23,30 +24,42 @@ export type List = {
   lastChat: Message;
 };
 
-type chatProps = {
+type ChatProps = {
   clickListBox: (customRoomId: string, userId: number, userName: string) => void;
   handleOpen: () => void;
   seller: {
     sellerId: number;
     shopName: string;
   };
+  user: UserInfo;
   product: {
     productId: number;
     productName: string;
   };
   isSeller: boolean;
+  role: string;
 };
 
-const ChatList = ({ handleOpen, clickListBox, seller, isSeller, product }: chatProps) => {
+const ChatList = ({
+  handleOpen,
+  clickListBox,
+  seller,
+  user,
+  isSeller,
+  product,
+  role,
+}: ChatProps) => {
   const [list, setList] = useState<List[]>([]);
-
   const [shopImg, setShopImg] = useState<string>('');
 
+  const message = useSSE(role, seller.sellerId, user.userId);
+
+  //TODO: 리액트쿼리로 변경하기
   const loadUserChatList: () => Promise<void> = async () => {
-    const sellerId = seller.sellerId;
-    userChatList(sellerId)
+    userChatList(seller.sellerId)
       .then((resData) => {
         const data = resData.chatList;
+        console.log('list', data);
         const img = resData.shopImage;
         setList([...data]);
         setShopImg(img);
@@ -62,6 +75,7 @@ const ChatList = ({ handleOpen, clickListBox, seller, isSeller, product }: chatP
     sellerChatList(sellerId, productId)
       .then((resData) => {
         const data = resData.chatList;
+        console.log('list', data);
         const img = resData.shopImage;
         setList([...data]);
         setShopImg(img);
@@ -77,10 +91,10 @@ const ChatList = ({ handleOpen, clickListBox, seller, isSeller, product }: chatP
   }, [isSeller]);
 
   return (
-    <div>
+    <>
       <ChatHeader shopName={seller.shopName} shopImg={shopImg} handleOpen={handleOpen} />
-      <ChatBody chatList={list} clickListBox={clickListBox} />
-    </div>
+      <ChatBody chatList={list} clickListBox={clickListBox} newMessage={message} />
+    </>
   );
 };
 
diff --git a/src/components/chat/chatList/ChatBody.tsx b/src/components/chat/chatList/ChatBody.tsx
index afe0aea..e75beed 100644
--- a/src/components/chat/chatList/ChatBody.tsx
+++ b/src/components/chat/chatList/ChatBody.tsx
@@ -1,13 +1,15 @@
 import { List } from '@/components/chat/ChatList';
 import ChatBox from '@/components/chat/chatList/ChatBox';
+import { ChatAlarm } from '@/hooks/useSSE';
 import * as S from '../Chat.styles';
 
 type ChatBodyProps = {
   chatList: List[];
   clickListBox: (customRoomId: string, userId: number, userName: string) => void;
+  newMessage?: ChatAlarm;
 };
 
-const ChatBody = ({ chatList, clickListBox }: ChatBodyProps) => {
+const ChatBody = ({ chatList, clickListBox, newMessage }: ChatBodyProps) => {
   return (
     <S.ChatBody>
       {chatList?.map((item, idx) => {
@@ -17,7 +19,11 @@ const ChatBody = ({ chatList, clickListBox }: ChatBodyProps) => {
             key={idx}
           >
             <ChatBox
-              lastChat={item.lastChat.content}
+              lastChat={
+                newMessage?.customRoomId === item.customRoomId
+                  ? newMessage?.content
+                  : item.lastChat.content
+              }
               sender={item?.lastChat.sender}
               productName={item.productName}
               image={item.imageUrl}
diff --git a/src/hooks/useSSE.ts b/src/hooks/useSSE.ts
new file mode 100644
index 0000000..c42f467
--- /dev/null
+++ b/src/hooks/useSSE.ts
@@ -0,0 +1,45 @@
+import { useEffect, useState } from 'react';
+
+export type ChatAlarm = {
+  content: string;
+  createAt: string;
+  customRoomId: string;
+  role: string;
+  sellerId: number;
+  sender: string;
+};
+
+//TODO: useSSE를 쓰는 컴포넌트에서 두번 렌더링 되는 이유 찾기.(최상단부터 뒤져보기)
+export const useSSE = (role: string, sellerId: number, userId: number) => {
+  const [message, setMessage] = useState<ChatAlarm>();
+
+  const isUser =
+    role === 'user'
+      ? `${import.meta.env.VITE_API_SSE_URL}/chat-alarm/${role}/${sellerId}/${userId}`
+      : `${import.meta.env.VITE_API_SSE_URL}/chat-alarm/${role}/${sellerId}`;
+
+  const [eventSource] = useState(() => new EventSource(isUser));
+
+  useEffect(() => {
+    console.log('되나', eventSource);
+    eventSource.addEventListener('sse', function (event) {
+      const message = JSON.parse(event.data);
+      console.log('새로운 채팅 알람: ', message);
+      setMessage({ ...message });
+    });
+
+    eventSource.onerror = function (error) {
+      console.error('EventSource failed:', error);
+      eventSource.close();
+    };
+
+    window.addEventListener('unload', function () {
+      if (eventSource) {
+        eventSource.close();
+        console.log('EventSource closed');
+      }
+    });
+  }, []);
+
+  return message;
+};