In order to figure out the oxidation behavior of steels during heating,five micro-alloyed steels were subjected to continuous and isothermal oxidation using the thermo gravimetric analyzer and the Gleeble-3500thermo-mechanical simulator.The microstructure of oxide scales,especially the thickness fractions of Fe2O3,Fe3O4 and FeO layers,was analyzed using the scanning electron microscope(SEM),electron probe microanalyzer(EPMA)and electron backscattered diffraction(EBSD)techniques.The micro-alloyed steels containing alloying elements(Si,Cr,Ni and Cu)show a higher oxidation resistance compared with the low carbon steel.It is found that alloying elements accumulated at scale/substrate interface during high temperature oxidation.Alloying elements function in two ways in the oxidation of steels:one is enhancing the scale/substrate interface and consequently suppressing the blister of scales;and the other is impeding the outward diffusion of iron cations from substrate to scales,resulting in the decrease of oxidation rate.As the diffusion of iron cations is impeded,the thickness fractions of Fe2O3 and Fe3O4of micro-alloyed steels are more than those of low carbon steels. In order to figure out the oxidation behavior of steels during heating, five micro-alloyed steels were subjected to continuous and isothermal oxidation using the thermo gravimetric analyzer and the Gleeble-3500thermo-mechanical simulator. Microstructure of oxide scales, especially the thickness fractions of Fe2O3, Fe3O4 and FeO layers, was analyzed using the scanning electron microscope (SEM), electron probe microanalyzer (EPMA) and electron backscattered diffraction (EBSD) techniques. Micro- alloyed steels containing alloying elements (Si, Cr, Ni and Cu) show a higher oxidation resistance compared with the low carbon steel .It is found that alloying elements accumulated at scale / substrate interface during high temperature oxidation. Alloying elements function in both ways in the oxidation of steels: one is enhancing the scale / substrate interface and : suppressing the blister of scales; and the other is impeding the outward diffusion of iron cations from substrate to scales, resulting in t he decrease of oxidation rate. As the diffusion of iron cations is impeded, the thickness fractions of Fe2O3 and Fe3O4 of micro-alloyed steels are more than those of low carbon steels.