A large number of ocean and harbor concrete structures have been in service for more than a century. However, the cost associated with repair of these structures damaged by corrosion of steel in concrete is a major maintenance expense for the owners. Due to wave and tidal action of sea water, these structures are divided into atmospheric, tidal, and submerged zones. The most devastating corrosion damage occurs at the splash area which is somewhere between the lower part of the atmospheric zone and upper part of the tidal zone. However, it is generally believed that steel corrosion in the submerged concrete is stifled because the oxygen concentration in the concrete is too low to sustain the corrosion activity. To investigate the corrosion mechanism in partially submerged concrete structures, the corrosion potentials, total corrosion current, and macro-cell corrosion current of the steel in concrete specimens were monitored. The results obtained from the three zones (submerged, tidal, and atmospheric zones) were compared and discussed.