Abstract: One of key requirements for the control mechanism in P2P systems is access control which becomes more critical when peers enter into or leave a collaboration community. However, the convential access control mechanism is not suitable because the P2P system is a decentralized and dynamic one. An approach is thus proposed for providing an efficient access control mechanism in hybrid P2P environments, i.e., it supports the role-based access control mechanism in a collaboration community comprising both leaf peers and super peers in hybrid P2P networks. Furthermore, to support access control among different communities, a trust-based access control mechanism is proposed so as to form a trustful cooperating environment. Compared to other existing approaches, the proposed one is content-based and fine-grained with the trust differences between peers taken into account, so highly applicable to hybrid P2P computing environments.