The rotor bar current in an induction motor (IM) is usually assumed to be sinusoidal. However, it is found that the rotor bar current may become non-sinusoidal even if the stator windings are fed with a sinusoidal source. Influence of air-gap length on the rotor bar current waveform of an IM, which is designed by using the same geometrical and operational parameters as the Toyota Prius 2010 interior permanent magnet machine, has been investigated in depth. It reveals that the air-gap length has a significant effect on the rotor bar current waveform, torque ripple, slot leakage, and efficiency. The conditions when the non-sinusoidal rotor bar current waveform occurs and the reasons behind this phenomenon are investigated by finite element method (FEM).