The electronic structures and compositions of the two oxide films on bulk nanocrystalline 304 stainless steel (BN-SS304) and its conventional polycrystalline counterpart (CP-SS304) after 30 days' immersion test in 0.5 mol/LHCl solution at room temperature were studied by X-ray photoelectron spectroscopy. The enhanced uniform and pitting corrosion resistances of BN-SS304 were attributed to the larger resistance and better chemical stability of the oxide film on BN-SS304, the less corrosion rate of Cr-0 for BN-SS304 and the larger atomic percentage of Cr3+ in the oxide film on BN-SS304. The larger resistance of oxide film on BN-SS304 resulted from the less state densities of valence electrons around Fermi level in the oxide film on BN-SS304. The better chemical stability of oxide film on BN-SS304 was attributed to (1) the larger binding energies of Fe2+ 2p3/2, Fe3+ 2p3/2 and Cr3+ 2p3/2 in the oxide film on BN-SS304; (2) the larger atomic percentages of Cr3+ and Fe2+ in the oxide film on BN-SS304. (C) 2013 Elsevier Ltd. All rights reserved.