Abstract 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 (icorr) 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 (η%) 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 (Ea) and thermodynamic parameters (ΔGads0, ΔHads0 and ΔSads0) 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.