In this study, a shape optimization of stiffener was conducted to increase buckling load or failure load in each case with a different design value and a different objective function for stiffened laminated composite panel of I-type under compression loading. Regarding each of buckling load or failure load as objective function, optimum design was carried out. In respect of optimum design, the effects of relative length of web and cab of stiffener on buckling load or failure load of postbuckling were investigated.