We apply the homogenization design method (HDM) to reduce the vibration level of a structure excited by magnetic harmonic force. We do this by obtaining the optimal material distribution of the structure to minimize the frequency response. We first use the Maxwell stress method to compute the magnetic force and then apply HDM for the optimization. Results show that the HDM can be used to minimize the frequency response. This method can also be applied to other rotary electrical devices such as motors and generators.