5-Benzoyl-4-(substitutedphenyl)-6-phenyl-3,4-dihydropyrimidine-2(1H)-(thio)ones (DHPMs) (I and II) were synthesized using the Biginelli three component cyclocondensation reaction of an appropriate arylaldehyde, and (thio) urea. The effect of these corrosion inhibitors on the corrosion of austenitic stainless steel in 0.5M H2SO4 has been studied by electrochemical methods using Tafel plot, linear polarization and electrochemical impedance spectroscopy at 298K. The inhibition efficiencies obtained from all the methods employed are in good agreement. The adsorption of the DHPMs onto the stainless steel surface was found to follow Langmuir and Dubinin-Radushkevich adsorption isotherm models. Negative values of Delta G(ads) in the acidic media ensured the Spontaneity Of the adsorption process. Results show DHPM I to be the best inhibitor with a mean efficiency of 91% at 2 x 10(-3) M additive concentration. (c) 2010 Elsevier B.V. All rights reserved.