Herein, it was studied the structural evolution of the AISI 1045 steel water-quenched and oilquenched, respectively, from a temperature higher than the critical to various temperatures between 800 and 820°C. The two quenching media were used at 16.5°C. Microstructural variations occurred in the quenched 1045 steel. Also, by using the four-terminal sensing, it was measured the evolution of the electrical resistivity of the quenched samples; it was found that quenching at different temperatures provoked a complex behavior. It was noticed a major increase in the electrical resistivity in the case of water-quenched samples. Besides, when compared samples before and after being heat-treated, via a metallographic analysis, it was showed an evolution of the phases of steel, what has a link with the evolution of the electrical resistivity, which was measured according to the increase of the austenitizing temperature.