The effects of C, Zr, Ti, and Nb on the oxidation resistance of 17% Cr steels have been investigated by means of isothermal heating and cyclic heating at temperatures up to 1000°C. It has been found that C has a detrimental effect on the oxidation resistance of 17% Cr steels. The oxidation behavior of steels containing Zr is different from that of steels containing Ti and Nb. Zr improves the oxidation resistance of 17% Cr steels to a great extent. Particularly, alloys containing Zr at a concentration which exceeds the stoichiometric equivalent of the total amount of C and N show excellent oxidation resistance up to 1000°C. Electron probe microanalysis shows the presence of a protective oxide layer consisting of Si‐rich oxide at the metal‐oxide interface, and no Zr is detected in the scales. With steels containing Ti and Nb, on the other hand, there is no protective Si‐rich oxide, but Ti and Nb are detected in the scales. These scales are not protective. As the effective factors of excellent oxidation resistance of Cr steels containing Zr, the behavior of carbide, grain growth, and phase transformation have been investigated.