A study of the ordinary mild steel/cooling water interface, with and without inhibitor. was carried Out using electrochemical impedance spectroscopy (EIS). EIS spectra in uninhibited medium reveal that a layer of corrosion and scale products is formed naturally and evolves with the immersion time. Monosaccharides derivatives were used as corrosion inhibitors. Most of them exhibit good behaviour against corrosion of ordinary steel in simulated water systems. Their inhibiting efficiency increases with concentration rise and depends on molecular structure especially -OH groups' position on two adjacent carbons and their number. In addition, the effect of MoO42- on the corrosion inhibition in the presence of the best inhibitor was also studied by EIS. The addition of MoO42- enhanced the inhibition efficiency. (C) 2009 Elsevier B.V. All rights reserved.