In this paper we estimate the effect of voltage unbalance on the losses in the core of the induction motor (IM). To measure losses in the core of the stator and the rotor, we used an IM with the rotor bars removed. We propose a test to estimate the equivalent resistance of the core losses and validate the results. We analyze the core losses for two severe voltage unbalanced conditions. The results show that the stator and the rotor core losses not change significantly with the voltage unbalance. The results also show that the positive-sequence voltage level affect the core losses of the IM more than the voltage unbalance.