A mobile ad hoc network is a collection of wireless mobile hosts forming a temporary network without the aid of any established infrastructure or centralized administration. The flexibility in space and time induces new challenges towards the security infrastructure. Contrary to their wired counterpart, mobile ad hoc networks do not have a clear line of defense, and every node must be prepared for encounters with an adversary. Therefore, a centralized or hierarchical network security solution does not work well. We provide scalable, distributed security architecture for mobile ad hoc networks in this paper. The architecture integrates the ideas of immune system and a multi-agent architecture. Compared with traditional security system, the proposed security architecture is designed to be distributed, autonomy, adaptability, scalability.