The present paper deals with the strength optimization of laminated composites under multiple loading based upon a mathematical programming method. A method using the transformed design variables with respect to the layer angles is proposed. In order to reduce the nonlinearity between the strength constraints and the layer angles, cos 2θ or sin 2θ is used as the design variable instead of using d directly. It is shown through several numerical examples that the present method gives reliable optimal results which are less sensitive to initial values used in the optimization.