Due to the massive existing vulnerabilities in mobile ad-hoc networks, they may be insecure against attacks by the malicious nodes. In this paper, the authors have analyzed the effects of Black hole attack on mobile ad hoc routing protocols. Mainly two protocols AODV and Improved AODV have been considered. Simulation has been performed on the basis of performance parameters and effect has been analyzed after adding Black-hole nodes in the network. Finally the results have been computed and compared to stumble on which protocol is least affected by these attacks.