Multicast authentication is a vital component in secure group communications, but authenticating real-time multicast streams over lossy channels or unreliable networks is very difficult due to the packet losses, expensive overheads and high delays. So this paper introduces a novel approach to multicast authentication based on LMCM (Layered Multiple Chaining Model). By the theoretical analyses, it is robust enough against packet losses, has low delays on the sender’s side and the receiver’s side. Both computation and communication overheads are in the reasonable scopes if its parameter values are determined systematically. And the high authentication probability can be achieved by increasing the number of packets that contain the hash of a previous packet and the number of hashes that are appended to the signature packets. Hence LMCM is secure, efficient and practical to more multicast applications than many previously proposed approaches.