The results of an investigation on the electrical resistivity of carbon steels are presented, and mathematical models which take into account the effect of the nonlinearities of the temperature and carbon content are proposed. The result showed that the electrical resistivity had a strong carbon content dependence within the range of 0.06-1.22 C wt.%. The sensitivity analysis of the model parameters indicated that a small perturbation of the electrical resistivity of carbon steels may attribute to enormous changes carbon content. A comparison between traditional formula and the regression equation on the relation of temperature and electrical resistivity in steels is provided.