Currently the characteristics of web services and the complexity of the distributed environment poses a great challenges for its security. Moreover, there is no complete Role Based Access Control (RBAC) model and RBAC framework for Web Services that has been reported in the current literature which considers spatio-temporal constraints in its model. So, in this work we propose a spatio-temporal RBAC model for providing effective access control for Web Services. In this model SOAP Proxy has been employed to send messages for Web Services and security mechanisms are provided using rules, temporal and spatial constraints. In the proposed model, users are restricted to assign the role and to access the service only when (s) he satisfies some predefined identity and spatio-temporal constraits in addition to the enforcement of usual security and integrity constraints which are used for providing additional security. Finally, we use intelligent agents to rpovide security through rules and constraints and hence multiple agents are deployed. ©2009 IEEE.