[Abstract] This paper proposes a new method to optimize the rotor structure in PM synchronous motors. The optimization process combines the topology optimization method and a constraint related to the shape of PMs, which accounts for manufacturing limitations. The rotor structures are designed considering two kinds of stator windings and two types of current driving methods. The obtained rotor structures are initially assumed to consist of four hexahedron PMs. The final shapes are obtained by a full search method.