In this work it will be presented the results of calculation of energy activation Q of selected industrial steels (e.g. grade 55 - carbon steel, LH15 – bearing steel, H10S2M, 4H14N14W2M and 50H21G9N4 valve steels) according to Polish Norm by two methods. In the first method the calculations of Q are based on the dependence of value of parabolic growth rate constants kp in function of reciprocal temperature. The second method is based on the calculated parameters, which allow to determine the value of Q for examined steels by using value of Q for pure iron, taken from literature data, and the particular values of mass concentrations of elements in oxidised steels. The growth kinetics of layers were almost according to parabolic law. The values of parabolic rate constant kp were calculated on the basis of measurements of thickness of oxide layers. To the experiment the cylindrical specimens were used. The isothermal process of oxidation was conducted in chamber furnace at 1100, 1060, 1020, 980 and 940°C in the air. Time of oxidation various from 3 till 1303.5 hrs. The comparison of obtained results of activation energy Q for mentioned methods of each individual examined steels gives a good agreement.