Oxidation layers formed on iron in deaerated bicarbonate/carbonate solutions at potentials in the active range were investigated through electrochemical techniques, FTIR and scanning electron microscopy. Three oxidation products have been obtained, siderite, am-FeOOH with adsorbed carbonate or bicarbonate ions and green rust GR1(CO3). It has been shown that the formation of either compound was strongly dependent on the concentration, temperature and pH of solutions.