Monitoring is a crucial factor for smooth run of distributed systems such as mobile agent based system. Various activities in such systems require monitoring such as performance analysis and tuning, scheduling strategies and fault detection. In this paper we present monitoring and fault tolerance technique for mobile agent based systems. We present mobile agent based fault prevention and detection technique where the team of mobile agents monitor each host in mobile agent based system. This research focuses on building an automatic, adaptive and predictive determining policy where critical host agents are identified in advance by monitoring agents, to avoid their failures. The novelty of proposed approach is constant collection and updating of local as well as global information of the system. This policy is determined by calculating weights; taking into account the criticality of the hosts by their monitoring agents which keep updating the weights of hosts. These weights act are used for decision making of checkpointing. These monitoring mobile agents act together to detect undesirable behaviors and also provide support for restoring the system back to normalcy. We also report on the result of reliability and performance issue of our proposed approach.