Influence of the irradiation on the corrosion behavior of stainless steel (type 304ULC) in boiling nitric acid solution was examined by using Co-60 gamma-ray source. It was found from the experimental results that radiolysis products of nitric acid (NOx, HNO2) resulted from the gamma-ray irradiation made the environment in the bulk solution more reducing one. On the other hand, corrosion rate of 304ULC was slightly enhanced by the irradiation, which being trivial from the engineering viewpoint. From the result of an AC impedance measurement, this corrosion enhancement was inferred as caused by an enhancement in the current across the passive film by the gamma-ray irradiation on the stainless steel surfaces.