A Mobile Ad-hoc NETwork (MANET) is an infrastructure-less autonomous system in which mobile nodes connected through wireless links are free to move randomly. The characteristics of MANET exhibit more vulnerability to communication related attacks. One of these attacks is Black hole attack. In this paper, the effect of black hole attack on the network performance is analyzed using AODV and IDSAODV routing protocols. A new protocol Improved IDSAODV (IIDSAODV) is also proposed that is a modification of IDSAODV protocol to reduce the effects of black hole attack.