An experimental study on the strength and deformation of concrete filled square box stub-columns is presented. Twelve specimens of concrete filled composite columns were tested under centric and eccentric static loading up to failure. Another steel hollow square box specimen was tested under centric static loading up to failure. Vertical stiffeners were used as shear connectors between concrete and steel
columns. Seven specimens were filled with normal strength concrete (30 MPa), while five specimens were filled with high strength concrete (65 to 90 MPa). The effect of strength of concrete, composite action between steel and concrete, and eccentricity of the load are considered in this study. Comparison between the experimental strength of the tested specimens and their predicated strength that calculated by several formulas was also presented. Considerable and beneficial recommendations to such composite columns were also given.