Robustness to parameter variation is required for rotor position sensorless control of a permanent magnet synchronous motor (PMSM) using a motor model. Therefore, various methods for measuring parameter variation or eliminating the influence of this variation have been proposed. This paper describes a rotor position sensorless control system of the PMSM that is based on a model reference adaptive system with a winding resistance and a back emf coefficient estimator. Only the winding resistance estimator minimizes the rotor position estimation error by compensating for the variation of the winding resistance and the back emf coefficient concurrently. Experimental results indicate that the winding resistance estimator is effective against both variations.