Advancement in wireless technologies and improved use of wireless devices demands more infrastructures-less networks like MANET (Mobile Ad hoc NETwork). Security of such a scenario is a challenging task over last few years. Because of its distinctive characteristics such as open medium and dynamic network topology, MANET can be accessible to malicious users. Black hole attack is one of serious threat in mobile ad hoc network, in which malicious node absorbs the packets instead of forwarding them to destination. In this paper, black hole attack in the network is detected and eliminated in two phases.