Wireless sensor network (WSN) has diverse field of applications, but on the other hand it is very much prone to the various security threats. There are number of attacks on wireless sensor networks like black hole attack, selective forwarding attacks, sink hole attack sybil attack etc. This paper concentrates on the performance of wireless sensor network in the presence of black hole attackers using Ad-hoc on Demand Distance Vector Routing Protocol (AODV). The black hole type of attacker node absorbs every message passing through it. So the affected node attacks the whole traffic in the network Further, the performance of sensor network using AODV with and without black hole attack is also analyzed. The simulation is done by using NS-2.35.