The buckling optimization of square rod composites with a given geometry subjected to uniaxial compression has been studied in terms of fiber volume fraction and thickness factor in the gradient structures by using a sequential linear Programming method. Discrete gradient structures in the designing of composites have shown some advantage of weight reduction in the design of composite structures with equivalent performance. Gradient structures have shown 12~18% reduction in gross fiber volume and 8-12% in weight compared to the uniform conventional homogeneous structures.