Abstract: Selfish nodes and malicious nodes in large-scale ad hoc networks lead to poor performance and even paralyze the network. How to dismiss these nodes from routing table is important to improve the network security. In this study, a security aware routing optimization algorithm named SARO is proposed to achieve this. The SARO is an improvement to ant optimization. It utilizes reputations from a reputation system to derive the pheromone trail refresh process and visible functions. Abnormal nodes are discarded from routing tables and packets are routed along paths with least abnormal nodes. The SARO is a security enhancement to routing protocols, which can both improve security of network and enhance the network performance.