Abstract: Effect of state doped acid,and feed molar ratio on corrosion performance of chemically prepared copolymer coating from aniline(AN)and N-ethylaniline(EA)has been investigated by open-circuit-potential(OCP)measurements.The results showed that the poly(anilineco-N-ethylaniline)coatings provided more effective corrosion protection to medium-carbon steel than the respective homopolymers,in which the copolymer coating with feed molar ratio of 20/80 possessed best anti-corrosion performance.The HCl doped coplymer showed better performance than the other acid doped coplymer.The dedoped coplymer showed better performance than doped coplymer.Especially in strong acid aqueous solution,the OCP value of the copolymer coposite coating with EA/AN dedoped copolymers as primer and epoxy resin as top coating did not decline but increase with soaking time.The enhancment in OCP reached to ca.110mV,which was positive shift ca.545mV based on bare steel,and positive shift ca.90mV based on polyaniline coating.After dipped in the corrosion media for half a year,the coatings were still smooth and did not peeled,and no blister and rust spot appeared.