Mobile ad-hoc network(MANET) is a wireless network which has robust infrastructure. Mobile nodes can be used to form MANET. Arbitrary topology can be formed by connecting nodes with each other randomly. When source want to transfer packets to destination, a path being discovered for transmission. Sometime packet get dropped in path due to malicious node. Attack by malicious node is called gray hole attack. In this paper we detect the gray hole attack in the MANET. The detection and removal of the malicious node depends on the calculated probability of each node.