Abstract: It is a method to appraise the life of a lightning rod using the “Modified Longevin Function” initially applied to represent the field and induction magnetic magnitudes in ferromagnetic materials modified properly to the inherent magnitudes of the characteristic curve of the lightning rods' varistors, current and voltage, measuring the variation of the parameters from the lightning rod model, using the adapted “Modified Langevin Function” through out the lightning rod life evaluating the lightning rod functional status based on the variation of the three parameters of the lightning rod varistor developed model; also using a lightning rod leakage current measurement system with techniques to get the share of the resistive current flowing through the varistor and with techniques to determine the parameters from the model that uses a software to meet the varistor model parameters.