The influence exerted by phenylthiourea(PTU) towards the corrosion of Fe79B16Si5 metallic glass in deaerated 0.1 N H2SO4 was investigated by direct-current (potentiodynamic polarization) and alternating-current (impedance spectroscopy) techniques. The inhibiting action found on the Fe79B16Si5 glassy alloy was compared to the corresponding one obtained on annealed polycrystalline Armco iron and on a previously tested Fe81B13.5Si3C2 amorphous alloy. The inhibitor film formed more rapidly and was more protective and stable on the amorphous alloys than on polycrystalline iron and a PTU concentration as low as 10(-5) M was sufficient to build instantaneously an efficient film on the surfaces of the metallic glasses. On these surfaces, a greater amount of PTU was chemisorbed than on the crystalline iron, an effect which leads to a more complete and protective film. © 2005 Elsevier B.V. All rights reserved.