Abstract: Privacy preservation of access control policy and credential for grid entities is an important aspect of grid security, whose importance has been increasingly highlighted with the wide application of grid technology. Using the theory of secure function evaluation, a circuit composition mechanism is proposed which adapts to the expression of composite policy, and a policy evaluation protocol is proposed based on oblivious transfer mechanism and scrambled circuit evaluation protocol; Using the theory of homomorphic encryption, an equility test protocol for attributes is proposed; Based on the two protocols, a privacy preserving protocol is proposed for the access control policies and credentials. Analysis shows that the proposed scheme can provide complete privacy preservation for the attributes of policy and credential, and also can avoid circle dependence problem caused by the related method.