The purpose of this paper is to propose a method for accurate estimation of the equivalent circuit parameters of induction motors at different operating regimes from a set of measurement data containing the rotor cage temperature and rotor resistance at 25 ∘C. Besides these rotor quantities, the method requires the measurement of supply voltage, stator current, frequency, speed, load torque, stator winding temperature and stator winding resistance at 25 ∘C. It is assumed that stator leakage reactance, core-loss resistance, friction and windage losses and stray load losses corresponding to the nominal operation are known. The proposed method iteratively determines air gap voltage, power factor and some other parameters. The effects of temperature change, frequency change, magnetic saturation and stray load losses are taken into consideration. The application of the method is discussed within the existing examples of five different motors. Excellent accuracy is achieved using the proposed method.