Constraints are an important aspect of role-based access control management (RBAC). Constraints have to be satisfied in user—role assignment and permission—role assignment. The importance of constraints associated with user-role assignments and permission-role assignments in RBAC has been recognized but the modelling of these constraints has not received much attention. In this chapter we use a de facto constraints specification language in software engineering to analyze the constraints in user-role assignments and permission-role assignments. Object Constraints Language (OCL), a part of the Unified Modelling Language (UML) widely used in object-oriented analysis and design is applied to express various constraints in RBAC. We analyse elements, relationships, constraints and structure of RBAC adopting class diagram method in UML. Then the representations of role-based access constraints such as separation, prerequisite, cardinality and mobility constraints with OCL are identified. Finally, comparisons with other related work and our future work are presented.