In this investigation, attempts have been made to study the inhibitive effect of N,N'-ortho-phenylen acetyle acetone imine (S 1) and 4-[(3-{[1-(2-hydroxyphenyl)methylidene]amino}propyl)ethanemidol]-1,3-ben zenediol (S2) in the concentration range of 50-400ppm for mild steel with two different microstructures resulted from two different heat treatments (annealed (A) and quenched and tempered (Q&T)) in I M hydrochloric acid solution. Both Schiff bases acted as a mixed type inhibitors. The S1 inhibitor for both microstructures showed better inhibition efficiency than S2. The A samples indicated slightly less corrosion than Q&T samples in I M HCl solution in absence of inhibitor due to the formation of duplex gamma-Fe2O3/Fe3O4. (C) 2009 Elsevier B.V. All rights reserved.