The use of the cosmetic ingredient cocamidopropylamine oxide (CAO) to inhibit the corrosion of steel in 0.5 mol/L HCl is investigated. Electrochemical and weight loss methods were used to evaluate the inhibiting effect of CAO and the influences of inhibitor concentration and temperature were determined. It was found that CAO acted as a mix-type inhibitor and was adsorbed chemically onto the steel in HCl solution, and the maximum inhibition efficiency was found at critical micelle concentration (CMC) of CAO in tested corrosive media. Moreover, it was speculated that relationships of the two adsorption sites of the inhibitor and steel surface were different. (C) 2016 Elsevier Inc. All rights reserved.