Abstract: In order to study the seismic performance of square concrete filled steel tubular (CFST) short columns, a total of 6 specimens with different cross-sectional sizes were tested under combined constant axial loading and cyclic lateral loading. The failure mode, hysteretic curves, skeleton curves and seismic performance indexes (e. g. stiffness degradation, energy dissipation, ductility, et al.) with different cross-section sizes were analyzed. Meanwhile, the nominal shear strength of specimens with different cross-section sizes was studied. The results indicate that the final failure modes, i.e., the bulge formed a complete ring on each side and the core concrete crushed at the same location, are similar for all columns with different cross-sectional sizes. The decline of nominal shear strength can be observed obviously as the structural size increases, i.e. the nominal shear strength decreases by 63.1% and 59.8% as the cross-section size varies from 200 mm to 600 mm under two opposite loading directions, indicating an obvious size effect; the relative nominal stiffness and the average energy dissipation coefficient decrease with the increase of structural size. The predicted values of shear strength formula that considers the size effect agree well with the tested values, implying this formula can be used to evaluate the shear capacity of square CFST short columns.