Abstract: An ad-hoc network is a collection of mobile nodes that dynamically form a temporary network and are infras- tructure less. Networks are protected using many firewalls and encryption softwares. But many of them are not sufficient and effective due to its limited power and mobility. The ultimate goal of the security solutions for wireless networks is to provide security services, such as authentication, confidentiality, in- tegrity, anonymity, and availability, to mobile users. Black hole attack is one of the severe security threats in ad-hoc networks which can be easily employed by exploiting vulnerability of on- demand routing protocols such as Ad-Hoc On Demand distance vector (AODV). In this paper, we have surveyed and compared the existing solutions to black hole attacks on AODV protocol.