This paper presents an accurate and efficient method for predicting the iron losses in PWM inverter-fed induction motors. The method was initially proposed for the prediction of iron losses in non-oriented soft magnetic material with the same supply conditions. The proposed method requires the separation of the iron losses in the hysteresis and eddy current components and the average rectified and RMS of the PWM voltage values. Starting from the iron losses measured with sinusoidal supply and the PWM waveform characteristics, a fast and reliable prediction of the iron losses in the motor with the new voltage supply can be obtained. The proposed method has been proved on an induction motor prototype capable of providing good accuracy in iron loss measurement. The comparison between the measured and predicted iron losses with PWM supply have shown excellent agreement, confirming the validity of the method.