The inhibition of the corrosion of carbon steel in 1 M HClO4 by 2-mercapto-1-methylimidazole (MMI) has been investigated in relation to the concn. of the inhibitor as well as the temp. using wt. loss and electrochem. measurements. The effect of the temp. on the corrosion behavior with addn. of different concns. of MMI was studied in the temp. range 30-60°C. Polarization curves reveal that MMI is a mixed type inhibitor. The inhibition efficiency of MMI is temp. independent but increases with the inhibitor concn. Changes in impedance parameters (charge transfer resistance, Rt, and double-layer capacitance, Cdl) were indicative of adsorption of MMI on the metal surface, leading to the formation of a protective film. Adsorption of MMI on the carbon steel surface is found to obey the Langmuir adsorption isotherm. Some thermodn. functions of dissoln. and adsorption processes were also detd. The XPS of the carbon steel indicated that MMI is chem. adsorbed on the steel surface. Moreover, the electronic properties such as HOMO (HOMO), LUMO (LUMO) energy levels and MO densities were calculated.