This paper proposes an approach for optimal placement of STATic synchronous COMpensator (STATCOM) in power systems. The approach is based on the simultaneous application of particle swarm optimization (PSO) and continuation power flow (CPF) to improve voltage profile, minimizing power system total losses, and for maximizing system loadability with respect to the size of STATCOM. Simulation results show the suitability of the PSO technique in finding multiple optimal solutions to the problem with reasonable computational effort. The installation of the STATOCM on these buses can increase the system voltage stability margin. The proposed technique is examined on the IEEE57 bus test system.