This paper describes the rotor design of high-speed permanent magnet (PM) synchronous motors considering rotor magnet and sleeve materials. The influence of four different sleeve materials with two different PM materials on the mechanical stress of a high-speed PM rotor is presented, and the relationship between sleeve thickness and shrink fit is examined. Rotor design criteria according to rotor materials are described by an analytical method. The proposed method is validated by an actual operational test at 400000 rpm using a fabricated prototype rotor.