There is no infrastructure in wireless ad hoc networks, and nodes independently manage the networks. Therefore, the connection between nodes is provided by the nodes themselves, and these nodes act as a router. In this case, they use routing protocol such as AODV. In order to provide the connections, nodes exchange data and control packages by trusting to each other. Since these networks have unique and special characteristics, they face with too much attack. One of these attacks is black hole attack in which destructive node attracts the network traffic, and destroys the packages. In this paper, black hole attack in AODV routing protocol has been investigated, and some solutions have been suggested. Simulation results indicate that, in proposed method, the rate of package delivery has been considerably increased in comparison with AODV.