The main objective of this paper is to investigate the enhancement of damping power system oscillations under various operating conditions with static synchronous compensator (STATCOM). The design of STACOM controller is formulated as an optimization problem and an modified invasive weed optimization (MIWO) algorithm is employed to search for optimal controller parameters settings. In this paper, a modified IWO algorithm with parallel probabilistic search method is applied for better convergence of the optimization process. The proposed controller is evaluated on a single machine infinite bus (SMIB) power system with STATCOM installed at mid point. To assess the effectiveness of the proposed design, eigen value analysis as well as time domain simulations are carried out to compare with results of genetic algorithm technique within MATLAB/SIMULINK environment.