In this study, experiments were conducted on five specimens of stiffened and unstiffened steel plate shear walls under cyclic loading. First, the specimens and frame design, material properties, and test setup were described. The behaviors of the unstiffened aluminum and steel infill plates were compared with three configurations of stiffened steel plate, i.e., cross-stiffened, circular-stiffened, and diagonally stiffened. The cross-sectional areas of the stiffeners were the same for all stiffened specimens. The results showed that the aluminum infill plate exhibited less ductility. By contrast, the unstiffened steel plate was very ductile, exhibiting a stable hysteresis curve and no tearing. The energy-absorption capacity of the steel plate shear walls increased for all stiffening configurations. Among all configurations, the cross-shaped stiffeners showed considerable increase in shear stiffness, ductility, and energy-dissipation capacity. The plate frame interaction method could predict the ultimate shear strengths of the unstiffened and cross-stiffened panels with good precision. The circular-stiffened steel shear wall seems to behave more desirably in high-amplitude displacements.