This paper describes a new mechanism for the discovery of a more efficient routing path in mobile multicast. When a mobile node (MN) moves to another foreign network, and it does not support multicast service, the multicast router discovery (MRD) mechanism enables the MN to forward multicast packets through using the most efficient routing path. Even when the multicast router does not operate due to any problem, the MRD mechanism enables multicast service to be supported on its network. Also, this paper describes a mechanism for the reduction of join latency due to re-subscription to multicast group.