The effects of tritiated water on the corrosion behavior of SUS304 stainless steel was studied using Tafel extrapolation method, one of electrochemical techniques with changing tritium concentration, dissolved oxygen concentration and pH in electrolyte as parameters. It was indicated that there would be two or more effects of tritium that enhance the corrosion of SUS304 stainless steel under several experimental conditions. One is passivation inhibitory effect, which could be observed only in highly corrosive circumstance of 1N H2SO4 electrolyte. The other effects of tritium on corrosion behavior could be observed not only in 1N H2SO4 but also incorrosive circumstance of 1N Na2SO4 electrolyte, which would be affected by dissolved oxygen concentration as well as tritium concentration.