Mobile ad-hoc networking (MANET) is a collection of mobile nodes that want to communicate to each others, but has no fixed links like wireless infrastructure networks to provide group applications and services. Therefore we need concern about providing each node with a secure and efficient key management system for dynamically discovering other nodes which can directly communicate with. Due to the network topology of an ad hoc network changes frequently and unpredictable, so the security of multicast routing becomes more challenging than the traditional networks. In this paper, we describe how any users in the multicast group can compose the group keys and propose a hierarchical group key management to securely multicast data from the multicast source to the rest of the multicast members in wireless ad hoc networks. This approach has a hierarchical structure where the group members are partitioned into rendezvous-location based clusters which can reduce the cost of key management. It not only provides the multicast routing information, but also fits the robustness of the wireless networks and reduces the overhead for the security management.