The Corrosion of reinforcing steels is a leading factor for the deterioration of concrete. In this study, partial substitution of cement with fly ash or blast furnace slag was made together with the addition of 4 different corrosion inhibitors, as a protective measure of reinforced concrete structures against corrosion of rebars. The effect of such incorporation of materials on corrosion of rebar was investigated under the alternating cycles of 12 hour immersion in artificial seawater and 12 hour drying in air. Electrochemical properties such as concrete resistance and corrosion rate were monitored with time through A.C. impedance spectroscopy and Tafel plot method. All test results showed consistently that the performance of the concretes are decreasing in following order, regardless of the corrosion inhibitors : the concretes with blast furnace slag, those with fly ash and those without slag or fly ash. The performance of each corrosion inhibitor showed a dependence on the types of concretes.