Multicast is a scalable solution for group communication. In order to offer security for multicast applications, a group key has to be changed whenever a member joins or leaves the group. This incurs 1-affect-n problem, which is a constraint on scalability. Decentralized approaches solve the scalability problem by dividing a group into subgroups that use independent group keys. These approaches, however, introduce new challenges: problem of trusting third party and inefficiency of data delivery. Proxy encryption is a good approach to solve the problem of trusting third party. In this paper, we propose a novel secure multicast scheme using the proxy cryptography. The proposed scheme provides not only scalability but also data transmission efficiency while third parties are not required to be trusted.