Corrosion inhibition of three imidazoline derivates with different numbers of benzcne rings,namely 2-phenyl-1-ethylamino imidazoline(CI-1),2-phcnyl-1-ethylamino-1-methylbenzyl quaternary imidazoline(CI-12) and 2-phcnyl-1-bcnzoyl ethylamino imidazoline(CI-13),on mild steel in CO2-saturated brine solution was evaluated by mass-loss method and potentiodynamic polarization method.The results show that the three imidazoline derivates can inhibit CO2 corrosion effectively with CI-12 ranking the highest.They mainly restrain the anodic dissolution and act as anodic-type inhibitors.The adsorptions of these derivates on the mild steel surface follow the Langmuir adsorption isothermal equation and belong to chemical adsorption.