With the development of Web Services, GIServices are gaining popularity in many geospatial applications. Although many studies on Web Service security has been done, the security issue of GIServices is still serious because of the specialties of GIS applications. In this paper, based on security principles of Web Services, we propose two methods to enhance GIService security. One is access control which includes spatial limitation, map scale limitation and temporal limitation, the other is encryption. With these extensions, GIServices can provide various geospatial functions in a more safely way.