A last-ply failure (LPF) analysis method for laminated composite plates is incorpo- rated into the ?nite element code-ANSYS, and a robust optimum design method is presented. The composite structure is analyzed by considering both in-plane and out-of-plane loads. For a lamina, two major failure modes are considered: matrix failure and ?ber breakage that are characterized by the proper strength criteria in the literature. When a lamina has failed, the laminate sti?ness is modi?ed to re?ect the damage, and stresses in the structure are re-analyzed. This procedure is repeatedly performed until the whole structure fails and thus the ultimate strength is determined. A structural optimization problem is solved with the ?ber orientation and the lamina thickness as the design variables and the LPF load as the objective. Finally, the robust optimum design method for laminates is presented and discussed. A last-ply failure (LPF) analysis method for laminated composite plates is incorpo- rated into the? Nite element code-ANSYS, and a robust optimum design method presented. The composite structure is analyzed by considering both in-plane and out- of-plane loads. For a lamina, two major failure modes are considered: matrix failure and? ber breakage that are characterized by the proper strength criteria in the literature. When a lamina has failed, the laminate sti? ness is modi? ed to re? ect the damage, and stresses in the structure are re-analyzed. A procedure optimization problem is solved with the? ber orientation and the lamina thickness as the design variables and the LPF load as the objective. Finally, the robust optimum design method for laminates is presented and discussed.