In order to withstand lateral loads such as wind and seismic loads, various systems have been proposed so far. Among these, one of the latest one is steel plate shear wall system that has been used in several high and important buildings in different seismic zones of countries including the United State and Japan. Comparing to other lateral load resisting systems such as braces and concrete shear walls, the steel plate shear walls have relative advantages. Additionally, a number of studies and experiences indicate that this type of shear wall has considerable strength and stiffness compared to other systems. Due to architectural requirements, openings are usually cut in panels of steel plate shear walls during construction. It is clear that the size and location of openings affect the performance of steel plate shear walls during earthquake. Therefore, two steel plate shear walls, one with stiffeners and other without stiffeners are considered and their performance are assessed under applying openings with different sizes. The shear walls are modeled in Abaqus and analyzed using finite element method to find the most critical opening size and location. For this reason, the entire plate of the shear wall is used; moreover, the force-displacement curves are obtained after the analysis to compare the shear walls performance.