Abstract. Role-based access control (RBAC) is recognized as an excellent model for access control in large-scale networked applications. Formalization of RBAC in a logical approach makes it feasible to reason about a specified policy and verify its correctness. We propose a formalization of RBAC by the description logic language ALCQ. We also show that the RBAC constraints can be captured by ALCQ. Furthermore, we demonstrate how to make access control decision, perform the RBAC functions as well as check the consistency of RBAC via the description logic reasoner RACER.