This paper presents three-dimensional shape optimization of inductors for the dc-dc converters, in which the nonconforming voxel-based finite element method (FEM) is employed to realize fast FE mesh generation during the optimization. The operating point of the inductor under the bias current condition, which is estimated from the circuit analysis, is obtained by nonlinear FE analysis. Then, the FE equation linearized around the operating point is solved being coupled with the circuit equation to obtain the magnetic fields in the inductor. The hysteresis loss is computed from the Steinmetz formula. Validity of the field computation is tested by comparing the numerical results with measured data. The multiobjective optimization of the inductor shapes is performed to minimize the winding resistance and hysteresis loss. It is shown that the present method can effectively find the Pareto solutions which can lead to improvement in the efficiency of the dc-dc converter.