Abstract: In unstructured Peer-to-Peer (P2P) systems such as Gnutella, the general routing search mechanism used is to blindly flood a query to the network among peers. However, the blindly flooding search mechanism makes the whole network subjected to distributed denial of service (DDoS) attacks. In order to alleviate or minimize the bad effect due to behavior of malicious nodes making use of the flooding search mechanism, we propose the Markov-based evaluation (ME) mechanism in which reputation is applied as incentive pattern called a trusted based incentive scheme. Trust based incentive is enabled by evaluating the transaction history of the peer and changing the peer's significance or capacity within the P2P network based on this evaluation. Our simulation study shows that this approach can effectively isolate the malicious peer and its message transmitting and improve resilience against DDoS attack.