Abstract. Multicast is an effective means for conducting the cooperative P2P communications. This paper studies an algorithm to construct a scalable and efficient end host multicast tree – Shared Cluster Tree (SCT). Compared with the previous work, by utilizing the underlying network properties, the novelty and contributions of our multicast algorithms are: (1) Scalability: by fully utilizing the underlying network properties to layer and cluster the group members, SCT decreases the transfer of the data traffic in the backbone domain links and therefore reserves more backbone domain resources to more local domains which include many more end hosts; (2) Efficiency: by searching the cluster cores based on the cluster core selection method, packets are multicasted to the cluster members by the cluster cores in the minimum delay. Our simulation results indicate that SCT is scalable and efficient for the end host multicast in P2P systems. . .