MANET is wireless network in which an end to end path is present between Network Security to MANET is wide problem. A black hole attack is an attack which drops the packets or provides wrong routing information to disturb routing process. In this paper we propose a new reputation based scheme to detect a black hole attack in MANET. In this scheme with the help of reputation of node we can detect the black hole nodes. For simulation ONE simulator is used. Keywords: MANET (Mobile Ad hoc Network), ONE (Opportunistic Network Environment) prophet, black hole, reputation
