—In an ad-hoc collaborative sharing environment, attribute-based access control provides a promising approach in defining authorization over shared resources based on users’ properties/attributes rather than their identities. While the user’s attributes are always asserted by different authorities in the form of credentials, these authorities may not be accepted by the resource owner with the same degree of trust. In this paper, we present a trust-aware role-based authorization framework, called RAMARS TM, to address both the access control and the trust management issues in such environment. Central to our approach is the dynamic role assignment based on a user’s attributes, and trust management, as a special constraint, is in place to make trust decisions on a user’s attributes. Required components and functions are identified and specified in our trust and access management policies. An architecture of prototype system implementation is also discussed.