A call admission control (CAC) scheme for 3G wireless networks based on the estimated interference and differentiated quality of service (QoS) is proposed in this paper. In this CAC scheme, the interferences introduced by the to-be-admitted new call and its impact to the QoS of the existing connections in the adjacent cells are considered in call admission. The purpose is to obtain QoS balance amongst neighboring cells within a cluster. Comparison of our proposed scheme with the current scheme without considering the effects of the to-be-admitted calls indicates that the proposed scheme performs better in outage and blocking probabilities.