The inhibition of mild steel corrosion in 1.0 M sulphuric acid by pyrimidine-2-thione derivatives (4,6-diphenyl-3,4-dihydropyrimidine-2(1H)-thione (PTH); 4-(4-methylphenyl)-6-phenyl-3,4-dihydropyrimidine-2(1H)-thione (PTM) and 4-(4-methoxyphenyl)-6-phenyl-3,4-dihydropyrimidine-2(1H)-thione (PTMO)) has been investigated using weight loss and electrochemical techniques (potentiodynamic polarization and electrochemical impedance spectroscopy (EIS)). All the compounds effectively hindered the corrosion process by becoming adsorbed on the metal surface, following the Langmuir isotherm. Computational studies were undertaken to provide mechanistic insight into the roles of the different substituents on the corrosion inhibition and adsorption behavior of the studied compounds.