Abstract An attempt has been made to depress the sorption of tritium on stainless steel. After the surface of the stainless steel was modified either by heating in air or by chemical passivation, the chemical properties of the modified surfaces were examined and the sorption phenomenon of tritium on the surface was studied. The thermal oxidation in air at 423–773 K caused the formation of a surface oxide layer consisting of about 90% of Fe(III) with a slight amount of Cr(IV) in an Fe 2O 3 CrO 2-lik state. The amount of tritium sorbed was found to be smaller on the above surface than on that oxidized at lower or higher temperature. The formation of a surface layer by chemical passivation led to an appreciable decrease in the amount of tritium sorbed. The depression of tritium sorption was attributed to the formation of a surface oxide layer constituted of an outer thin layer of Cr(III) Fe(II) in the Cr 2O 3 FeO-like state and an inner layer of CrO 2-like Cr(IV) with metallic Fe(0) and Ni(0).