Ubiquitous computing is characterized by freedom of movement in both time and location, which means users expect to receive services anytime and anywhere. Therefore, the security service should consider the factor of
. As a basic authorization service mechanism, RBAC has been used in the security community for access control model. In order to apply RBAC to ubiquitous computing environment, it is necessary to add both location and time dimension. In this paper, we propose new access control model supporting time and location dimensions. The proposed access control model can effectively support various ubiquitous computing environments.