diff --git a/src/main/java/com/example/tripmingle/adapter/out/ChatPersistAdapter.java b/src/main/java/com/example/tripmingle/adapter/out/ChatPersistAdapter.java
index 07146712..273f61b6 100644
--- a/src/main/java/com/example/tripmingle/adapter/out/ChatPersistAdapter.java
+++ b/src/main/java/com/example/tripmingle/adapter/out/ChatPersistAdapter.java
@@ -6,6 +6,7 @@
 
 import com.example.tripmingle.dto.req.chat.GetAllChatMessageReqDTO;
 import com.example.tripmingle.entity.ChatMessage;
+import com.example.tripmingle.entity.ChatRoomType;
 import com.example.tripmingle.port.out.ChatPersistPort;
 
 import lombok.RequiredArgsConstructor;
@@ -14,7 +15,7 @@
 @RequiredArgsConstructor
 public class ChatPersistAdapter implements ChatPersistPort {
 
-	// private final ChatRepository chatRepository;
+	private final ChatRepository chatRepository;
 
 	@Override
 	public Slice<ChatMessage> getChatMessages(GetAllChatMessageReqDTO getAllChatMessageReqDTO, Pageable pageable) {
@@ -28,4 +29,10 @@ public Slice<ChatMessage> getChatMessages(GetAllChatMessageReqDTO getAllChatMess
 	public void save(ChatMessage chatMessage) {
 
 	}
+
+	@Override
+	public Long getChatMessagesCount(ChatRoomType chatRoomType, Long chatRoomId) {
+		// return chatRepository.countByChatRoomIdAndChatRoomType(chatRoomId, chatRoomType);
+		return null;
+	}
 }
diff --git a/src/main/java/com/example/tripmingle/application/facadeService/ChatRoomFacadeService.java b/src/main/java/com/example/tripmingle/application/facadeService/ChatRoomFacadeService.java
index 70790030..8b087148 100644
--- a/src/main/java/com/example/tripmingle/application/facadeService/ChatRoomFacadeService.java
+++ b/src/main/java/com/example/tripmingle/application/facadeService/ChatRoomFacadeService.java
@@ -1,11 +1,14 @@
 package com.example.tripmingle.application.facadeService;
 
+import static com.example.tripmingle.common.constants.Constants.*;
+
 import java.util.List;
 
 import org.springframework.stereotype.Service;
 
 import com.example.tripmingle.application.service.BoardService;
 import com.example.tripmingle.application.service.ChatRoomService;
+import com.example.tripmingle.application.service.ChatService;
 import com.example.tripmingle.application.service.UserService;
 import com.example.tripmingle.dto.req.chat.EnterGroupChatRoomReqDTO;
 import com.example.tripmingle.dto.req.chat.EnterOneOnOneChatRoomReqDTO;
@@ -32,14 +35,17 @@
 public class ChatRoomFacadeService implements ChatRoomUseCase {
 
 	private final ChatRoomService chatRoomService;
+	private final ChatService chatService;
 	private final BoardService boardService;
 	private final UserService userService;
 
-	private ChatRoomUser generateChatRoomUserEntity(Long chatRoomId, Long userId, ChatRoomType chatRoomType) {
+	private ChatRoomUser generateChatRoomUserEntity(Long chatRoomId, Long userId, ChatRoomType chatRoomType,
+		Long chatFirstIndex) {
 		return ChatRoomUser.builder()
 			.chatRoomId(chatRoomId)
 			.user(userService.getUserById(userId))
 			.chatRoomType(chatRoomType)
+			.chatFirstIndex(chatFirstIndex)
 			.build();
 	}
 
@@ -54,13 +60,12 @@ public EnterOneOnOneChatRoomResDTO enterOneOnOneChatRoom(EnterOneOnOneChatRoomRe
 				.user2(contactUser)
 				.build();
 			OneOnOneChatRoom savedOneOnOneChatRoom = chatRoomService.saveOneOnOneChatRoom(oneOnOneChatRoom);
-
 			ChatRoomUser currentChatRoomUser = generateChatRoomUserEntity(savedOneOnOneChatRoom.getId(),
-				currentUser.getId(), ChatRoomType.ONE_ON_ONE);
+				currentUser.getId(), ChatRoomType.ONE_ON_ONE, FIRST_ENTER_CHAT_ROOM_CHAT_COUNT);
 			chatRoomService.joinOneOnOneChatRoom(currentChatRoomUser);
 
 			ChatRoomUser contactChatRoomUser = generateChatRoomUserEntity(savedOneOnOneChatRoom.getId(),
-				contactUser.getId(), ChatRoomType.ONE_ON_ONE);
+				contactUser.getId(), ChatRoomType.ONE_ON_ONE, FIRST_ENTER_CHAT_ROOM_CHAT_COUNT);
 			chatRoomService.joinOneOnOneChatRoom(contactChatRoomUser);
 		} else {
 			oneOnOneChatRoom = chatRoomService.getOneOnOneChatRoomByUserIds(currentUser.getId(), contactUser.getId());
@@ -83,16 +88,20 @@ public EnterGroupChatRoomResDTO enterGroupChatRoom(EnterGroupChatRoomReqDTO ente
 				.user(board.getUser())
 				.chatRoomId(groupChatRoom.getId())
 				.chatRoomType(ChatRoomType.GROUP)
+				.chatFirstIndex(FIRST_ENTER_CHAT_ROOM_CHAT_COUNT)
 				.build();
 			chatRoomService.joinGroupChatRoom(chatRoomMasterUser);
 		} else {
 			groupChatRoom = chatRoomService.getGroupChatRoomByBoardId(enterGroupChatRoomReqDTO.getBoardId());
 		}
 		if (!chatRoomService.existsUserInChatRoom(user.getId())) {
+			Long alreadyExistsChatCount = chatService.getChatMessagesCount(ChatRoomType.GROUP, groupChatRoom.getId());
 			ChatRoomUser chatRoomUser = ChatRoomUser.builder()
 				.chatRoomId(groupChatRoom.getId())
 				.user(user)
 				.chatRoomType(ChatRoomType.GROUP)
+				.chatFirstIndex(
+					alreadyExistsChatCount == 0 ? FIRST_ENTER_CHAT_ROOM_CHAT_COUNT : alreadyExistsChatCount - 1)
 				.build();
 			chatRoomService.joinGroupChatRoom(chatRoomUser);
 		}
diff --git a/src/main/java/com/example/tripmingle/application/service/ChatService.java b/src/main/java/com/example/tripmingle/application/service/ChatService.java
index baeab556..4b2c338a 100644
--- a/src/main/java/com/example/tripmingle/application/service/ChatService.java
+++ b/src/main/java/com/example/tripmingle/application/service/ChatService.java
@@ -6,6 +6,7 @@
 
 import com.example.tripmingle.dto.req.chat.GetAllChatMessageReqDTO;
 import com.example.tripmingle.entity.ChatMessage;
+import com.example.tripmingle.entity.ChatRoomType;
 import com.example.tripmingle.port.out.ChatPersistPort;
 
 import lombok.RequiredArgsConstructor;
@@ -17,7 +18,10 @@ public class ChatService {
 	private final ChatPersistPort chatPersistPort;
 
 	public Slice<ChatMessage> getChatMessages(GetAllChatMessageReqDTO getAllChatMessageReqDTO, Pageable pageable) {
-		return chatPersistPort.getChatMessages(getAllChatMessageReqDTO, pageable);
+		return null;
 	}
 
+	public Long getChatMessagesCount(ChatRoomType chatRoomType, Long chatRoomId) {
+		return chatPersistPort.getChatMessagesCount(chatRoomType, chatRoomId);
+	}
 }
diff --git a/src/main/java/com/example/tripmingle/common/constants/Constants.java b/src/main/java/com/example/tripmingle/common/constants/Constants.java
index 2044bd06..4e4d5efc 100644
--- a/src/main/java/com/example/tripmingle/common/constants/Constants.java
+++ b/src/main/java/com/example/tripmingle/common/constants/Constants.java
@@ -8,4 +8,5 @@ public class Constants {
 	public static String SORT_CREATING_CRITERIA = "createdAt";
 	public static String SORT_ID_CRITERIA = "id";
 	public static Long NO_PARENT_COMMENT_ID = -1L;
+	public static Long FIRST_ENTER_CHAT_ROOM_CHAT_COUNT = 0L;
 }
diff --git a/src/main/java/com/example/tripmingle/entity/ChatRoomUser.java b/src/main/java/com/example/tripmingle/entity/ChatRoomUser.java
index f57164d4..344b1d25 100644
--- a/src/main/java/com/example/tripmingle/entity/ChatRoomUser.java
+++ b/src/main/java/com/example/tripmingle/entity/ChatRoomUser.java
@@ -39,11 +39,14 @@ public class ChatRoomUser extends BaseEntity {
 
 	private boolean connectionState;
 
+	private Long chatFirstIndex;
+
 	@Builder
-	public ChatRoomUser(User user, Long chatRoomId, ChatRoomType chatRoomType) {
+	public ChatRoomUser(User user, Long chatRoomId, ChatRoomType chatRoomType, Long chatFirstIndex) {
 		this.user = user;
 		this.chatRoomId = chatRoomId;
 		this.chatRoomType = chatRoomType;
+		this.chatFirstIndex = chatFirstIndex;
 	}
 
 	public void exitChatRoom() {
diff --git a/src/main/java/com/example/tripmingle/port/out/ChatPersistPort.java b/src/main/java/com/example/tripmingle/port/out/ChatPersistPort.java
index 48f062f0..d2e3ade6 100644
--- a/src/main/java/com/example/tripmingle/port/out/ChatPersistPort.java
+++ b/src/main/java/com/example/tripmingle/port/out/ChatPersistPort.java
@@ -5,6 +5,7 @@
 
 import com.example.tripmingle.dto.req.chat.GetAllChatMessageReqDTO;
 import com.example.tripmingle.entity.ChatMessage;
+import com.example.tripmingle.entity.ChatRoomType;
 
 public interface ChatPersistPort {
 
@@ -12,4 +13,5 @@ public interface ChatPersistPort {
 
 	void save(ChatMessage chatMessage);
 
+	Long getChatMessagesCount(ChatRoomType chatRoomType, Long chatRoomId);
 }