Abstract: A mobile ad-hoc network （MANET） is a multi-hop temporary communication network of mobile nodes equipped with wireless transmitters and receivers without the aid of any current network infrastructure. MANETs have its fundamental characteristics, such as open medium, dynamic topology, distributed cooperation, and constrained capability. In MANETs environment, nodes depend on each other for routing and forwarding packets. Cooperation among nodes is a key issue in such an environment. However, some of the nodes in MANETs may behave selfishly, and not forward packets to save battery and other resources. Since nodes in MANETs communicate with each other without any central authority （which can monitor selfish behavior of nodes）, a centralized solution to stimulate cooperation is not suitable. In this paper, game theory is used to study nodes behavior when nodes receive service based on their reputation. Reputation is employed as a mechanism to incite nodes to share resource and forward packets for other nodes. A trust model is proposed based game theory to encourage packets forwarding and discipline selfish behavior in MANETs. Simulation results show the proposed trust model can successfully identify selfish nodes and build trust among trust nodes to improve the efficiency of MANETs.