This paper presents a procedure to minimize the cost of materials of cable-stayed bridges with composite box girder and concrete tower. Two sets of iterations are included in the proposed procedure. The first set of iteration performs the structural analysis for a cable-stayed bridge. The second set of iteration performs the optimization process. The design is formulated as a general mathematical problem with the cost of the bridge as the objective function and bending forces, shear forces, fatigue stresses, buckling and deflection as constraints. The constraints are developed based on the Canadian National Standard CAN/CSA-S6-88. The finite element method is employed to perform the complicated nonlinear structural analysis of the cable-stayed bridges. The internal penalty function method is used in the optimization process. The limit states design method is used to determine the load capacity of the bridge. A computer program written in FORTRAN 77 is developed and its validity is verified by several practical-sized designs.