The surface chloride ion concentration (C0) and apparent diffusion coefficient (Dcip) arc very important parameters on estimating the deterioration of RC structures in marine environments. In this study, concrete specimens with an inhibitor were exposed to different marine environments for 1, 3, and 5 years. These encompasscd both tidal and splash environments at three ports in Japan. C0 and Dap were obtained from the chloride ion profiles in concrete. Saturation rates of concrete were also tested. Using the long-term exposure test results, the effects of the exposure environments and periods on C0 and Dap were studied. The results are shown below: 1) Co did not increase between 3 and 5 years in a large number of cases. These specimens tended to show a high saturation rate. A high saturation rate was considered to lead to almost no change in C0 over time. 2) Dap in the tidal environment was slightly larger than in the splash environment. This was considered to be due to the higher saturation rate of concrcte in the tidal than splash environment.