This paper describes the implementation of reliable group communication in Java. The underlying delivery mechanism for multicast is presently based on User Datagram Protocol (UDP) that provides a “best effort” delivery service. Best effort implies that IP packets are treated with essentially equal weight, and while IP makes an effort to deliver all packets to their destination, packets may occasionally be delayed, lost, duplicated, or delivered out of order. One of multicast’s weaknesses is its lack of reliability due to its use of UDP for data transmission. Reliable transmission means that there should be no packet loss, no disordering and no duplication of packets at the receiver side. The focus of this paper is to implement Reliable Multicast using Java, which is mainly used for one-to-many connections. This work focuses on reliable multicast in a local area network (LAN) environment. The reliability has been introduced at application layer and is receiver’s initiated, NACK (negative acknowledgement) based.