Because of their crucial role in protecting power electronic equipment against over-voltages and transients, metal oxide varistors (MOV) represent a key component of the electrical system. Although improper heat dissipation and internal temperature rises can lead to a significant decrease in performance or even to a wear-out failure of the MOV, there are very few studies in the literature describing the thermal modeling of varistors. Thus, in this paper, an instantaneous loss and thermal modeling procedure for MOV under a standard current surge mission profile is proposed. Initially, the specification and characteristics of a study-case varistor are presented, followed by a detailed description of the electro-thermal modeling procedure. Afterwards, the thermal behavior of the MOV is investigated and the differences between the heating and cool-down thermal models are highlighted. Finally, in order to validate the proposed electrothermal models, the temperature of the varistor is measured with an infrared camera. The experimental measurements are in well agreement with the simulation results, and thus, providing an initial validation of the proposed modeling procedure.