Although many researches in distributed database area perceive that the only practical way to construct a distributed database system from already existing local heterogeneous database systems is to integrate them by guaranteeing local site autonomy, an efficient update synchronization scheme for the system has not been developed so far. Furthermore, most previous concurrency control schemes for heterogeneous systems failed to guarantee site autonomy or global serializability. In this paper, we propose a concurrency control scheme that guarantees both global serializability of concurrent transaction execution and site autonomy for heterogeneous distributed database systems.