The sand play technique has often been used in psychological treatments or in the diagnosis of autism patients. In this paper, the prototype application called “virtual sand box” is developed as a virtual environment to support this technique. Experimental results show the advantages of applying virtual reality technology to clinical medicine; particularly with respect to the diagnosis of people with psychological and psychiatrical difficulties such as autism and neurosis. The actual system has been implemented by using a graphics workstastion, a wide-view filed display, and 3D input devices.