Mobile ad-hoc networks (MANET) are self-configuringwireless networks without any particular infrastructure. MANET’s are highly vulnerable to attacks due to continuously changing network topology, lack of central monitoring and lack of efficient defense mechanism. Selfish nodes in MANET’s are the defective nodes which drop the packets that are not intended to them and presence of these nodes will impact on performance degrade of MANET’s. In this paper, DSR (Dynamic Source Routing)protocol is used and a malicious selfish node is introduced in the network to analyze the selfish node attack and a prevention algorithm for selfish node attack is also suggested. Network parameters meters like throughput, end to end delay and packet delivery ratio are used for evaluation and comparison. Simulation tool used in this paper is NS2. © Research India Publications.