The inhibitive properties of a drug, phenytoin (5,5-diphenylimidazolidine-2,4-dione, 5DID), on corrosion of low-carbon steel (LCS) in aerated 1 M H 2 SO 4 solution has been evaluated in this study using gravimetric and polarization measurements. Judging from the results obtained, the drug served as a good inhibitor for LCS. The inhibition efficiency (I %) of 5DID in this medium was found to be concentration and temperature dependent, and the adsorption data fit the Langmuir and Temkin isotherm models. Polarization curves revealed that 5DID specifically affected the anodic reaction of the corrosion process. The electrochemical and gravimetric results were complemented with atomic force microscopy surface characterization.