To minimize the leakage of microwave which can occur when one pulls the door of a microwave oven during its operation, shape optimization of the door frame is presented. A numerical optimization is implemented to minimize the dynamic twisting deformation of the door frame. Shape design variables are defined, which represent the dimension of the bead in the flange. Two optimal design problems are established to minimize the maximum twisting deformation from harmonic response analysis. The problems are solved, their results being compared and evaluated.