Electrochemical corrosion behavior and hydrogen evolution reaction of weld aged maraging steel have been investigated, in 1.0 M sulfuric acid solution containing different concentrations of 2-(4-chlorophenyl)-2-oxoethyl benzoate (CPOB). The data obtained from polarization technique showed that the corrosion current density (i(corr)) and the hydrogen evolution rate decrease, indicating a decrease in the corrosion rate of weld aged maraging steel as well as an increase in the inhibition efficiency (eta%) with the increase in inhibitor concentration. Changes in impedance parameters were indicative of adsorption of CPOB on the metal surface, leading to the formation of protective film. Both activation (E-a) and thermodynamic parameters (Delta G(ads)(0), Delta H-ads(0) and Delta S-ads(0)) were calculated and discussed. The adsorption of CPOB on the weld aged maraging steel surface obeyed the Langmuir adsorption isotherm model. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) study confirmed the formation of an adsorbed protective film on the metal surface. Copyright (C) 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.