This paper presents a decentralized control system using multi-agent technology to prevent voltage collapse of a large power system following a catastrophic event involving multiple contingencies. The proposed automatic control system is employed to identify the affected region by the disturbances and to activate timely countermeasures. The modified IEEE-57 bus test power system has been used for simulation and the simulation was done in PSAT software. The multi-agent system has been implemented in Java language using JADE (Java Agent Development Framework). The results from the case studies indicate the efficiency of the proposed approach.