Abstract: An imidazolinyl-quaternary ammonium salts inhibitor (MIQ) with multi-activated sites was synthesized from p-(dimethylamino)-benzoic acid, diethylenetriamine and benzyl chloride. The synthesized inhibitor was characterized by FTIR. The anti-corrosion performance of the compound on mild steel was investigated in 6% hydrochloric acid using a mass loss method. Effecting factors of the anti-corrosion performance such as concentration, temperature and contact time were discussed. The results show that the inhibitive efficiency of the inhibitor can reach 97% when the concentration of MIQ is 0.5% and the inhibition efficiency undergoes a decrease trend with the increase of temperature and immersion time. After combined with KSCN, KI and so on, the resultant complexes significantly improve the inhibition efficiency. The adsorption of MIQ on the steel follows a Langmuir adsorption isotherm. The absorbed MIQ forms a thin film on of the mild steel and efficiently prevents its direct contact with the acidic detergent reagent.