The influence of linear copolymer of amines and formaldehyde namely poly(aniline-formaldehyde) (Inh1), poly(o-toluidene-formaldehyde) (Inh2), and poly(p-chloroaniline-formaldehyde) (Inh3) on corrosion of mild steel in hydrochloric acid was evaluated by weight loss measurements, linear polarization, Tafel polarization, and electrochemical impedance spectroscopy. These polymers showed very high inhibition efficiency at very low concentrations. Results obtained showed that all inhibitors are mixed inhibitors and participate in reaction probably in the form of metal inhibitor complex on metal surface. Atomic force microscopic studies reveal that the surface of metal is quite unaffected after use of inhibitor in hydrochloric acid solution. (c) 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011