2-Hydroxyphenyl-5-mercapto-1-oxa-3,4-diazole (HMO), 2-phenyl-5-mercapto-1-oxa-3,4-diazole (PMO), and 2-cinnamyl-5-mercapto-1-oxa-3,4-diazole (CMO) were synthesized in the laboratory and their influence on the inhibition of corrosion of mild steel in I N HCl and 1 N H2SO4 was investigated by weight loss and potentiodynamic polarization techniques. The inhibition efficiency (IE) of these compounds was found to vary with concentration, temperature and immersion time. Good IE was evidenced in both acid solutions. The adsorption of these compounds on mild steel surface for both acids were found to obey Temkin's adsorption isotherm. The potentiodynamic polarization data have shown that compounds studied predominantly behaves as cathodic inhibitors in both acid solutions. (C) 2002 Elsevier Science B.V. All rights reserved.