This paper proposes a purpose-based framework for supporting privacy preserving access control policies and mechanisms. The mechanism enforces access policy to data containing personally identifiable information. The key component of the framework is purpose involved access control models (PAC) that provide full support for expressing highly complex privacy-related policies, taking into account features like purposes and conditions. A policy refers to an access right that a subject can have on an object, based on attribute predicates, obligation actions, and system conditions. Policy conflicting problems may arise when new access policies are generated. The structure of purpose involved access control policy is studied, and efficient conflict-checking algorithms are developed. Finally a discussion of our work in comparison with other access control and frameworks such as EPAL is presented.