As mobile web services becomes more pervasive, applications based on mobile web services will need flexible access control mechanisms. Unlike traditional approaches based on the identity or role for access control, access decisions for these applications will depend on the combination of the required attributes of users and the contextual information. This paper proposes a semantic context-based access control model (called SCBAC) to be applied in mobile web services environment by combining semantic web technologies with context-based access control mechanism. The proposed model is a context-centric access control solutions, context is the first-class principle that explicitly guides both policy specification and enforcement process. In order to handle context information in the model, this paper proposes a context ontology to represent contextual information and employ it in the inference engine. As well as, this paper specifies access control policies as rules over ontologies representing the concepts introduced in the SCBAC model, and uses semantic web rule language (SWRL) to form policy rule and infer those rules by JESS inference engine. The proposed model can also be applied to context-aware applications.