CSCW systems introduce new requirements for access control, which cannot be met by using existing models. A new role-based access control model, RBCSAC (role-based collaborative systems access control), is introduced to meet these requirements. This model formally describes the relationship among the key elements of access control such as data, operation, privilege, role and user. It provides the method for recording access control information. The model grants and revokes access privileges of cooperative users by assigning them some roles and canceling their roles. Two role-assignment rules and two checking rules of operation legality are also provided. RBCSAC model is brought forward aiming at accommodating to the characteristics of collaborative systems such as multi-user, interaction, collaboration, real-time, dynamic.