The ever-increasing multicast data applications recently have aroused considerable interests in the design of congestion control scheme for multicast services. This kind of study is indeed important, especially to those multicast receivers with large propagation delays which mean the feedbacks arriving at the source node are somewhat outdated and harmful to control actions. A distributed self-tuning explicit rate algorithm is presented in this paper to overcome the vulnerability that suffers from the heterogeneous multicast receivers. It is suggested that congestion controllers be located at the source and the participating intermediate nodes to regulate the transmission rate. This network-assisted property is different from the traditional control scheme in that the router computes the appropriate transmission rate of itself and executes it rather than sends packets in best efforts. This active manner makes the control more responsive to the network status. The proposed self-tuning controller has essentially a proportional controller structure. The proportional gain is related to the extent that the router buffer occupancy deviates from the desired point. Simulation results show the efficiency of the proposed scheme in terms of fast response, high link utilization, and relatively stable buffer occupancy.