In this article Model Reference Adaptive System (MRAS) based estimator of a rotor resistance of an induction motor (IM) was presented. In contrast to the solutions know from the literature, the reference model of this estimator uses the measured values of the phase current and adaptive part is a virtual current sensor. The article presents an accu-rate description of the algorithm taking into account the discrete equations, for a possible practical implementation in the microprocessor system. In first step the impact of motor parameters to stator current estimation quality in the adaptive model was checked. Subsequently simulation tests of the proposed rotor resistance estimator were carried out for the field-oriented control of the induction motor drive system with a model of an induction motor with fixed pa-rameters and for an induction motor with a changing main inductance according to a magnetization curve. Analysis of the estimator's work showed its high efficiency and insensitivity to changes in the IM main inductance.