Inhibition effect of three novel nonionic surfactants based on oleic acid monoamide namely ET-5, ET-20 and ET-40 against corrosion of steel in 1M HCl was investigated by weight loss and electrochemical measurements. Scanning electron microscopy (SEM) and energy dispersion X-ray (EDX) were used to characterize the steel surface. The results showed that these surfactants act as a corrosion inhibitor in acidic medium and their inhibition efficiencies depend to the ethylene oxide content in the system. Adsorption of these surfactants on steel surface was found to obey Langmuir’s adsorption isotherm. The thermodynamic parameters K_ads and ΔG°_ads are calculated and discussed.