diff --git a/src/modules/project/repositories/project.repository.js b/src/modules/project/repositories/project.repository.js
index 5b941cf..e2c989c 100644
--- a/src/modules/project/repositories/project.repository.js
+++ b/src/modules/project/repositories/project.repository.js
@@ -390,6 +390,32 @@ class ProjectRepository {
       data: { status },
     });
   }
+
+  async findActiveMembershipsByUserIds(userIds) {
+    return prisma.projectMember.findMany({
+      where: {
+        id_user: {
+          in: userIds.map((id) => parseInt(id)),
+        },
+        status: "active",
+      },
+      include: {
+        user: {
+          select: {
+            id: true,
+            full_name: true,
+            email: true,
+          },
+        },
+        project: {
+          select: {
+            id: true,
+            project_name: true,
+          },
+        },
+      },
+    });
+  }
 }
 
 module.exports = new ProjectRepository();
diff --git a/src/modules/project/services/project.service.js b/src/modules/project/services/project.service.js
index d1775d1..a5c64a0 100644
--- a/src/modules/project/services/project.service.js
+++ b/src/modules/project/services/project.service.js
@@ -58,6 +58,27 @@ class ProjectService {
         }
       }
 
+      const userIds = users.map((user) => user.id);
+
+      if (userIds.length > 0) {
+        const activeMemberships = await projectRepository.findActiveMembershipsByUserIds(userIds);
+
+        if (activeMemberships.length > 0) {
+          const assignedInterns = activeMemberships.map((membership) => {
+            const email = membership.user?.email || "unknown email";
+            const projectName = membership.project?.project_name || "Unknown Project";
+
+            return `${email} already assigned to ${projectName}`;
+          });
+
+          return error(
+            new ConflictError(
+              `One or more interns already have an active project: ${assignedInterns.join(", ")}`
+            )
+          );
+        }
+      }
+
       const newProjectData = {
         id_admin: parseInt(actor.id),
         project_icon: projectData.project_icon,
@@ -69,7 +90,6 @@ class ProjectService {
         status: "active",
       };
 
-      const userIds = users.map((user) => user.id);
       const project = await projectRepository.createWithMembers(
         newProjectData,
         userIds,
@@ -441,7 +461,7 @@ class ProjectService {
         const activeMembership = intern.project_members?.[0] || null;
         const projectName = activeMembership?.project?.project_name || "Unassigned";
         const role = intern.lamaran_magang?.lowongan_magang?.posisi || "-";
-        
+
         return {
           id: intern.id,
           name: intern.full_name,
diff --git a/src/routes/project.routes.js b/src/routes/project.routes.js
index 49655f9..a695391 100644
--- a/src/routes/project.routes.js
+++ b/src/routes/project.routes.js
@@ -74,6 +74,7 @@ const router = express.Router();
  *           example: 2026-08-10
  *         member_emails:
  *           type: array
+ *           description: Optional intern emails to invite. Each intern must already have an active user account and must not be assigned to another active project.
  *           items:
  *             type: string
  *             format: email
@@ -459,7 +460,7 @@ const router = express.Router();
  * /project-api/add:
  *   post:
  *     summary: Create a new project
- *     description: Create a new Internify LMS project. Admin can optionally invite interns by email.
+ *     description: Create a new Internify LMS project. Admin can optionally invite interns by email. Invited interns must not be active members of another project.
  *     tags: [Project]
  *     security:
  *       - bearerAuth: []