In the present paper, the buckling behavior of box-shaped, pultruded fiber reinforced polymetric members under axial compression is investigated. For long-columns, elastic general buckling behavior has first been observed, and ultimate stresses are in good agreement with Euler buckling criterion. At a large deflection equilibrium state, it is shown to observe periodically wavy buckling dents at its compression flange. The ultimate stresses for short-columns are in good agreement with the local buckling criterion obtained by using the present orthotropic thin-walled plate buckling theory. The acoustic emission measurement has suggested that the collapse is started from the micro-damage caused by the development of elastic local buckling dent.