Abstract: Data replication is widely used in data grids, where the placement of replicas to achieve the optimal performance is a major problem worth studying. Based on a general data grid model represented by an undirected connected graph, an algorithm named quality of service （QOS）-replica placement algorith (RPA) is proposed to place the replicas while individual QoS constraints are still met. The proposed QoS aware replica placement algorithm can find the replica placements while the communication cost in the system is the minimum. The conducted experiments through simulation show the feasibility and effectiveness of the proposed algorithm.