The corrosion inhibition of mild steel in 0.5 M sulfuric acid solutions by some new synthesized organic compounds namely (E)-2-acetyl-3-(butyl amino)-N-phenyl buten-2-thioamide (compound A), (E)-3-(4-(dimethyl amino) phenyl amino)-2-acetyl-N-phenyl buten-2-thioamide (compound 13) and (E)-3-(2,3-dimethyl phenyl amino)-2-acetyl-N-phenyl buten-2-thioamide (compound C) was investigated using weight loss and potentiostatic polarization techniques. These measurements reveal that the inhibition efficiency obtained by these compounds increased by increasing their concentration. The inhibition efficiency follows the order A > B > C. Polarization studies show that these compounds are of the mixed-type but dominantly act as an anodic inhibitors for steel in 0.5 M H2SO4 solutions. These inhibitors function through adsorption following Langmuir isotherm. Activation energy and Gibbs free energy for adsorption of inhibitors are calculated. Molecular modeling has been conducted to correlate the corrosion inhibition properties with the calculated quantum chemical parameters. (C) 2009 Elsevier B.V. All rights reserved.