diff --git a/apps/chat/services/message_service.py b/apps/chat/services/message_service.py
index e69de29b..951e6976 100644
--- a/apps/chat/services/message_service.py
+++ b/apps/chat/services/message_service.py
@@ -0,0 +1,51 @@
+from django.core.exceptions import PermissionDenied, ValidationError
+from django.db import IntegrityError
+
+from apps.chat.models import ChatMessage
+from apps.study_groups.models import GroupMember, StudyGroup
+from apps.users.models import User
+
+
+class MessageService:
+    # 메시지 생성 및 단건 조회 기능 제공
+
+    @staticmethod
+    def validate_member(study_group: StudyGroup, user: User) -> None:
+        # 해당 사용자가 그룹 구성원이 맞는지 검증
+        is_member = GroupMember.objects.filter(
+            study_group_id=study_group.id,
+            user_id=user.id,  # mypy 오류로 user 대신 user.id를 넘겼습니다.
+        ).exists()
+
+        if not is_member:
+            raise PermissionDenied("그룹 멤버만 메시지를 작성할 수 있습니다.")
+
+    @staticmethod
+    def create_message(
+        study_group: StudyGroup,
+        user: User,
+        content: str,
+    ) -> ChatMessage:
+
+        if not content or not content.strip():
+            raise ValidationError("메시지 내용은 비어 있을 수 없습니다.")
+
+        MessageService.validate_member(study_group, user)
+
+        try:
+            return ChatMessage.objects.create(
+                study_group=study_group,
+                sender=user,
+                content=content.strip(),
+            )
+        except IntegrityError:
+            raise ValidationError("메시지를 생성할 수 없습니다.")
+
+    @staticmethod
+    def get_message(message_id: int) -> ChatMessage:
+        msg = ChatMessage.objects.select_related("sender").filter(id=message_id).first()
+
+        if msg is None:
+            raise ValidationError("메시지를 찾을 수 없습니다.")
+
+        return msg
diff --git a/apps/chat/tests/test_chatroom_service.py b/apps/chat/tests/test_chatroom_service.py
new file mode 100644
index 00000000..57822200
--- /dev/null
+++ b/apps/chat/tests/test_chatroom_service.py
@@ -0,0 +1,151 @@
+import time
+
+from django.core.exceptions import PermissionDenied
+from django.test import TestCase
+
+from apps.chat.models.chat_message import ChatMessage
+from apps.chat.models.last_read_message import LastReadMessage
+from apps.chat.services.chatroom_service import ChatRoomService
+from apps.study_groups.models import GroupMember, StudyGroup
+from apps.users.models.users import User
+
+
+class TestChatRoomService(TestCase):
+
+    def setUp(self) -> None:
+        # 사용자
+        self.user = User.objects.create(
+            email="user@example.com",
+            name="김오즈",
+            nickname="테스트",
+            phone_number="01012345678",
+            gender="M",
+            birthday="1999-01-01",
+        )
+
+        self.other_user = User.objects.create(
+            email="hayeong@example.com",
+            name="송하영",
+            nickname="ha0",
+            phone_number="01012341234",
+            gender="F",
+            birthday="1997-09-29",
+        )
+
+        # 스터디 그룹
+        self.group = StudyGroup.objects.create(
+            name="Django Study",
+            introduction="스터디 소개",
+            max_headcount=5,
+            start_at="2025-12-01T00:00:00Z",
+            end_at="2025-12-30T00:00:00Z",
+        )
+
+        # user만 그룹 멤버로 등록
+        GroupMember.objects.create(
+            study_group_id=self.group,
+            user_id=self.user,
+            is_leader=True,
+        )
+
+        # 테스트용 메시지 생성
+        self.msg1 = ChatMessage.objects.create(
+            study_group=self.group,
+            sender=self.user,
+            content="첫 번째 메시지",
+        )
+        time.sleep(0.001)  # 생성 시간 차이를 내려고 넣었습니다
+
+        self.msg2 = ChatMessage.objects.create(
+            study_group=self.group,
+            sender=self.user,
+            content="두 번째 메시지",
+        )
+
+    # 멤버 검증 테스트
+    def test_validate_member_success(self) -> None:
+        # 그룹에 속한 사용자는 검증 통과
+        ChatRoomService.validate_member(self.group, self.user)
+
+    def test_validate_member_fail(self) -> None:
+        # 그룹에 속하지 않은 사용자는 PermissionDenied
+        with self.assertRaises(PermissionDenied):
+            ChatRoomService.validate_member(self.group, self.other_user)
+
+    def test_get_messages(self) -> None:
+        # 해당 그룹의 메시지 목록을 시간순으로 반환
+        messages = ChatRoomService.get_messages(self.group, self.user)
+        self.assertEqual(messages.count(), 2)
+
+    def test_get_room_info(self) -> None:
+        info = ChatRoomService.get_room_info(self.group, self.user)
+        self.assertEqual(info["group_id"], self.group.id)
+        self.assertEqual(len(info["members"]), 1)
+        self.assertEqual(info["members"][0]["nickname"], self.user.nickname)
+
+    def test_mark_all_read(self) -> None:
+        ChatRoomService.mark_all_read(self.group, self.user)
+
+        record = LastReadMessage.objects.get(
+            study_group=self.group,
+            user=self.user,
+        )
+        self.assertEqual(record.message.id, self.msg2.id)
+
+    def test_mark_all_read_no_messages(self) -> None:
+        # 메시지가 전혀 없는 새로운 그룹 생성
+        empty_group = StudyGroup.objects.create(
+            name="Empty Group",
+            introduction="메시지 없음",
+            max_headcount=5,
+            start_at="2025-12-01T00:00:00Z",
+            end_at="2025-12-30T00:00:00Z",
+        )
+
+        GroupMember.objects.create(
+            study_group_id=empty_group,
+            user_id=self.user,
+            is_leader=True,
+        )
+
+        # 실행
+        ChatRoomService.mark_all_read(empty_group, self.user)
+
+        # 메시지가 없으면 last_read 레코드도 x
+        record = LastReadMessage.objects.filter(
+            study_group=empty_group,
+            user=self.user,
+        ).first()
+
+        self.assertIsNone(record)
+
+    def test_get_chatrooms_basic(self) -> None:
+        # 채팅방 목록 조회 기본 테스트
+        result = ChatRoomService.get_chatrooms(self.user)
+
+        self.assertEqual(len(result), 1)
+
+        room = result[0]
+
+        # 그룹 id 검증
+        self.assertEqual(room["group_id"], self.group.id)
+
+        # 그룹 이름 검증
+        self.assertEqual(room["group_name"], self.group.name)
+
+        # last_read x -> unread count = 전체 메시지 개수
+        total_messages = ChatMessage.objects.filter(study_group=self.group).count()
+
+        self.assertEqual(room["unread_count"], total_messages)
+
+    def test_get_chatrooms_with_last_read(self) -> None:
+        LastReadMessage.objects.create(
+            study_group=self.group,
+            user=self.user,
+            message=self.msg1,
+        )
+
+        result = ChatRoomService.get_chatrooms(self.user)
+
+        self.assertEqual(len(result), 1)
+        self.assertEqual(result[0]["unread_count"], 1)
diff --git a/apps/chat/tests/test_last_read_service.py b/apps/chat/tests/test_last_read_service.py
new file mode 100644
index 00000000..d778d646
--- /dev/null
+++ b/apps/chat/tests/test_last_read_service.py
@@ -0,0 +1,105 @@
+from django.core.exceptions import PermissionDenied
+from django.test import TestCase
+
+from apps.chat.models.chat_message import ChatMessage
+from apps.chat.models.last_read_message import LastReadMessage
+from apps.chat.services.last_read_service import LastReadService
+from apps.study_groups.models import GroupMember, StudyGroup
+from apps.users.models.users import User
+
+
+class TestLastReadService(TestCase):
+
+    def setUp(self) -> None:
+        # 사용자
+        self.user = User.objects.create(
+            email="test@example.com",
+            name="김오즈",
+            nickname="테스터",
+            phone_number="01012345678",
+            gender="M",
+            birthday="1999-01-01",
+        )
+
+        self.other_user = User.objects.create(
+            email="hayeong@example.com",
+            name="송하영",
+            nickname="ha0",
+            phone_number="01012341234",
+            gender="F",
+            birthday="1997-09-29",
+        )
+
+        self.group = StudyGroup.objects.create(
+            name="Django Study",
+            introduction="스터디 소개",
+            max_headcount=5,
+            start_at="2025-12-01T00:00:00Z",
+            end_at="2025-12-30T00:00:00Z",
+        )
+
+        GroupMember.objects.create(
+            study_group_id=self.group,
+            user_id=self.user,
+            is_leader=True,
+        )
+
+        self.message1 = ChatMessage.objects.create(
+            study_group=self.group,
+            sender=self.user,
+            content="메시지 1",
+        )
+
+        self.message2 = ChatMessage.objects.create(
+            study_group=self.group,
+            sender=self.user,
+            content="메시지 2",
+        )
+
+    def test_update_last_read_create(self) -> None:
+        # 처음 읽을 경우 LastReadMessage 생성
+        LastReadService.update_last_read(
+            study_group=self.group,
+            user=self.user,
+            message=self.message1,
+        )
+
+        record = LastReadMessage.objects.filter(
+            study_group=self.group,
+            user=self.user,
+        ).first()
+
+        self.assertIsNotNone(record)
+        assert record is not None
+        self.assertEqual(record.message.id, self.message1.id)
+
+    def test_update_last_read_update(self) -> None:
+        # 이미 읽은 과거가 있으면 제일 최신 메시지로 업데이트
+
+        LastReadMessage.objects.create(
+            study_group=self.group,
+            user=self.user,
+            message=self.message1,
+        )
+
+        LastReadService.update_last_read(
+            study_group=self.group,
+            user=self.user,
+            message=self.message2,
+        )
+
+        updated = LastReadMessage.objects.get(
+            study_group=self.group,
+            user=self.user,
+        )
+
+        self.assertEqual(updated.message.id, self.message2.id)
+
+    def test_update_last_read_fail_other_user(self) -> None:
+        # 그룹 구성원이 아니라면 PermissionDenied
+        with self.assertRaises(PermissionDenied):
+            LastReadService.update_last_read(
+                study_group=self.group,
+                user=self.other_user,
+                message=self.message1,
+            )
diff --git a/apps/chat/tests/test_message_service.py b/apps/chat/tests/test_message_service.py
new file mode 100644
index 00000000..5d02c0ea
--- /dev/null
+++ b/apps/chat/tests/test_message_service.py
@@ -0,0 +1,89 @@
+from django.core.exceptions import PermissionDenied, ValidationError
+from django.test import TestCase
+
+from apps.chat.models.chat_message import ChatMessage
+from apps.chat.services.message_service import MessageService
+from apps.study_groups.models import GroupMember, StudyGroup
+from apps.users.models.users import User
+
+
+class TestMessageService(TestCase):
+
+    def setUp(self) -> None:
+        # 사용자 생성
+        self.user = User.objects.create(
+            email="test@example.com",
+            name="김오즈",
+            nickname="테스터",
+            phone_number="01012345678",
+            gender="M",
+            birthday="1999-01-01",
+        )
+
+        self.other_user = User.objects.create(
+            email="hayeong@example.com",
+            name="송하영",
+            nickname="ha0",
+            phone_number="01012341234",
+            gender="F",
+            birthday="1997-09-29",
+        )
+
+        # 스터디 그룹 생성
+        self.group = StudyGroup.objects.create(
+            name="Django Study",
+            introduction="스터디 소개",
+            max_headcount=5,
+            start_at="2025-12-01T00:00:00Z",
+            end_at="2025-12-30T00:00:00Z",
+        )
+
+        # 그룹 멤버 등록
+        GroupMember.objects.create(
+            study_group_id=self.group,
+            user_id=self.user,
+            is_leader=True,
+        )
+
+    # 메시지 생성 테스트
+    def test_create_message_success(self) -> None:
+        """그룹 멤버는 정상적으로 메시지 생성 가능"""
+
+        msg = MessageService.create_message(study_group=self.group, user=self.user, content="안녕하세요!")
+
+        self.assertIsInstance(msg, ChatMessage)
+        self.assertEqual(msg.content, "안녕하세요!")
+        self.assertEqual(msg.sender_id, self.user.id)
+
+    def test_create_message_fail_for_non_member(self) -> None:
+        # 그룹 멤버가 아니면 PermissionDenied 발생
+
+        with self.assertRaises(PermissionDenied):
+            MessageService.create_message(study_group=self.group, user=self.other_user, content="멤버가 아닙니다")
+
+    def test_create_message_fail_empty_content(self) -> None:
+        # 빈 메시지 내용이면 ValidationError 발생
+
+        with self.assertRaises(ValidationError):
+            MessageService.create_message(study_group=self.group, user=self.user, content="   ")
+
+    # 메시지 단일 조회 테스트
+    def test_get_message_success(self) -> None:
+        """단일 메시지 조회 성공"""
+
+        msg = ChatMessage.objects.create(
+            study_group=self.group,
+            sender=self.user,
+            content="조회 테스트",
+        )
+
+        found = MessageService.get_message(msg.id)
+
+        self.assertEqual(found.id, msg.id)
+        self.assertEqual(found.content, "조회 테스트")
+
+    def test_get_message_not_found(self) -> None:
+        # 없는 메시지를 조회하면 ValidationError 발생
+
+        with self.assertRaises(ValidationError):
+            MessageService.get_message(9999)