diff --git a/server/__tests__/appointment/rejection.reason.test.ts b/server/__tests__/appointment/rejection.reason.test.ts
new file mode 100644
index 0000000..9490e60
--- /dev/null
+++ b/server/__tests__/appointment/rejection.reason.test.ts
@@ -0,0 +1,229 @@
+import { AppointmentService } from "../../src/services/appointment/appointment.service.js";
+import { AppointmentModel } from "../../src/db/schemes/appointmentSchema.js";
+import {
+  createTestAppointment,
+  createTestStudent,
+  createTestTeacher,
+} from "../helpers/test.helpers.js";
+import {
+  setupTestDatabase,
+  teardownTestDatabase,
+} from "../setup/database.setup.js";
+import { container } from "../../src/composition/compositionRoot.js";
+import { TYPES } from "../../src/composition/composition.types.js";
+
+describe("Appointment Rejection Reason", () => {
+  let appointmentService: AppointmentService;
+  let studentId: string;
+  let teacherId: string;
+
+  beforeAll(async () => {
+    await setupTestDatabase();
+    appointmentService = container.get<AppointmentService>(
+      TYPES.AppointmentService,
+    );
+
+    const student = await createTestStudent();
+    const teacher = await createTestTeacher();
+    studentId = student.id;
+    teacherId = teacher.id;
+  });
+
+  afterAll(async () => {
+    await teardownTestDatabase();
+  });
+
+  beforeEach(async () => {
+    await AppointmentModel.deleteMany({});
+  });
+
+  describe("Rejection Reason Validation", () => {
+    it("should require rejection reason when rejecting appointment", async () => {
+      const appointment = await createTestAppointment(studentId, teacherId);
+
+      await expect(
+        appointmentService.updateAppointmentStatus(appointment.id, {
+          status: "rejected",
+        }),
+      ).rejects.toThrow(
+        "Rejection reason is required when rejecting an appointment",
+      );
+    });
+
+    it("should reject reason with less than 100 characters", async () => {
+      const appointment = await createTestAppointment(studentId, teacherId);
+      const shortReason = "Too short";
+
+      await expect(
+        appointmentService.updateAppointmentStatus(appointment.id, {
+          status: "rejected",
+          rejectionReason: shortReason,
+        }),
+      ).rejects.toThrow(
+        "Rejection reason must be between 100 and 500 characters",
+      );
+    });
+
+    it("should reject reason with more than 500 characters", async () => {
+      const appointment = await createTestAppointment(studentId, teacherId);
+      const longReason = "A".repeat(501);
+
+      await expect(
+        appointmentService.updateAppointmentStatus(appointment.id, {
+          status: "rejected",
+          rejectionReason: longReason,
+        }),
+      ).rejects.toThrow(
+        "Rejection reason must be between 100 and 500 characters",
+      );
+    });
+
+    it("should accept valid rejection reason (100-500 characters)", async () => {
+      const appointment = await createTestAppointment(studentId, teacherId);
+      const validReason =
+        "This is a valid rejection reason that meets the minimum character requirement of 100 characters. The student did not provide sufficient information about their learning goals and objectives for this lesson.";
+
+      const result = await appointmentService.updateAppointmentStatus(
+        appointment.id,
+        {
+          status: "rejected",
+          rejectionReason: validReason,
+        },
+      );
+
+      expect(result).toBeDefined();
+      expect(result?.status).toBe("rejected");
+      expect(result?.rejectionReason).toBe(validReason);
+    });
+
+    it("should not require rejection reason for approved status", async () => {
+      const appointment = await createTestAppointment(studentId, teacherId);
+
+      const result = await appointmentService.updateAppointmentStatus(
+        appointment.id,
+        {
+          status: "approved",
+        },
+      );
+
+      expect(result).toBeDefined();
+      expect(result?.status).toBe("approved");
+      expect(result?.rejectionReason).toBeNull();
+    });
+
+    it("should not require rejection reason for pending status", async () => {
+      const appointment = await createTestAppointment(studentId, teacherId);
+
+      const result = await appointmentService.updateAppointmentStatus(
+        appointment.id,
+        {
+          status: "pending",
+        },
+      );
+
+      expect(result).toBeDefined();
+      expect(result?.status).toBe("pending");
+      expect(result?.rejectionReason).toBeNull();
+    });
+  });
+
+  describe("Rejection Reason Storage", () => {
+    it("should store rejection reason in database", async () => {
+      const appointment = await createTestAppointment(studentId, teacherId);
+      const rejectionReason =
+        "This appointment is rejected because the student did not provide adequate preparation materials and the requested time slot conflicts with another commitment.";
+
+      await appointmentService.updateAppointmentStatus(appointment.id, {
+        status: "rejected",
+        rejectionReason,
+      });
+
+      const updatedAppointment = await AppointmentModel.findOne({
+        id: appointment.id,
+      });
+
+      expect(updatedAppointment?.status).toBe("rejected");
+      expect(updatedAppointment?.rejectionReason).toBe(rejectionReason);
+    });
+
+    it("should retrieve rejection reason when fetching appointment", async () => {
+      const appointment = await createTestAppointment(studentId, teacherId);
+      const rejectionReason =
+        "The requested lesson topic requires more advanced preparation than the student's current level allows. Please complete prerequisite materials first.";
+
+      await appointmentService.updateAppointmentStatus(appointment.id, {
+        status: "rejected",
+        rejectionReason,
+      });
+
+      const retrievedAppointment = await appointmentService.getAppointmentById(
+        appointment.id,
+      );
+
+      expect(retrievedAppointment?.status).toBe("rejected");
+      expect(retrievedAppointment?.rejectionReason).toBe(rejectionReason);
+    });
+  });
+
+  describe("Edge Cases", () => {
+    it("should handle exactly 100 characters", async () => {
+      const appointment = await createTestAppointment(studentId, teacherId);
+      const exactReason = "A".repeat(100);
+
+      const result = await appointmentService.updateAppointmentStatus(
+        appointment.id,
+        {
+          status: "rejected",
+          rejectionReason: exactReason,
+        },
+      );
+
+      expect(result?.status).toBe("rejected");
+      expect(result?.rejectionReason).toBe(exactReason);
+    });
+
+    it("should handle exactly 500 characters", async () => {
+      const appointment = await createTestAppointment(studentId, teacherId);
+      const exactReason = "A".repeat(500);
+
+      const result = await appointmentService.updateAppointmentStatus(
+        appointment.id,
+        {
+          status: "rejected",
+          rejectionReason: exactReason,
+        },
+      );
+
+      expect(result?.status).toBe("rejected");
+      expect(result?.rejectionReason).toBe(exactReason);
+    });
+
+    it("should handle 99 characters (should fail)", async () => {
+      const appointment = await createTestAppointment(studentId, teacherId);
+      const shortReason = "A".repeat(99);
+
+      await expect(
+        appointmentService.updateAppointmentStatus(appointment.id, {
+          status: "rejected",
+          rejectionReason: shortReason,
+        }),
+      ).rejects.toThrow(
+        "Rejection reason must be between 100 and 500 characters",
+      );
+    });
+
+    it("should handle 501 characters (should fail)", async () => {
+      const appointment = await createTestAppointment(studentId, teacherId);
+      const longReason = "A".repeat(501);
+
+      await expect(
+        appointmentService.updateAppointmentStatus(appointment.id, {
+          status: "rejected",
+          rejectionReason: longReason,
+        }),
+      ).rejects.toThrow(
+        "Rejection reason must be between 100 and 500 characters",
+      );
+    });
+  });
+});