The role of chromium contents on atmospheric corrosion of steel in the environment containing chloride ion was studied by exposure test and electrochemical experiments. It was found that corrosion resistance of 1 chromium steel was lower than that of the steel without chromium in the environment whose concentration of chloride ion was very high by the exposure test. On the other hand, containing chromium increases corrosion resistance in the environment with low chloride concentration. In neutral chloride solution corrosion rate of 1 chromium steel was lower than that of the steel without chromium, but was high in low pH chloride solution. The pH dependence of corrosion resistance of 1 chromium steel corresponded with the corrosion resistance by the exposure test.