The paper describes a cooperative design system for 3D virtual scene. The objective of the system is to allow multiple users to design a 3D scene cooperatively via communication network. The system is based on a distributed layered architecture. At the application layer, a 3D cooperative design tool is implemented. The basic cooperative design operations include reading and saving a 3D scene, selecting an object from the common 3D scene, modification of the objects by geometrical transformations, modification of the attributes of the global scene or an individual object, such as, object texture, material, illumination parameters, etc. A special protocol (SMI) has been designed and implemented for the communication with peer cooperative design tool situated on peer hosts. The session control layer and group communication layer form the cooperative support platform for the system. The session control layer is responsible for the tasks required by a cooperative working session such as service multiplexing, data consistency control, member admission etc. The group communication layer provides the point to point or point to multipoint communication. The experimental system is currently implemented on Silicon Graphics hardware platform with an 100MB/s internal network. Open Inventor has been used for the 3D design tool. The data format is fully VRML compatible.