This paper analyzes the effect of Park transformation on the stability of the Permanent Magnet Synchronous Motor Control (PMSM) sensorless control system. In the sensorless control method, the transformation from a-p to the d-q frame can cause problems, especially stability issues. System stability is analyzed in two ways. They are stability analysis with and without taking the frame transformation into account. The sensorless control system that will be analyzed uses MRAS as the observer and Proportional Integral (PI) as a current controller. When analyzing without taking the frame transformation into account, it is proved that the sensorless control system of PMSM is stable, but when analyzing with taking the frame transformation into account, the system can be unstable. The transformation can cause estimation errors. The error can cause the stability problems, too. It is proved that the system can be unstable when the estimated position value differs from the actual position.