The polypyrrole and polyaniline copolymer coating (PPy-PAni) and PPy-PAni doped with sodium molybdate copolymer coating ( ) were synthesized on stainless steel by cyclic voltammetry. The effect of molybdate on the passivation of stainless steel was investigated by linear sweep voltammetry in 0.2 mol L−1 of oxalic acid. The corrosion prevention performances of these copolymer coatings for stainless steel were investigated by linear sweep voltammetry, electrochemical impedance spectroscopy in 1 mol L−1 of sulfuric acid, and potentiodynamic polarization in 0.1 mol L−1 of hydrochloric acid. Copolymer coating doped with molybdate could accelerate the formation of the passive oxide film and have better corrosion prevention efficiencies than PPy-PAni coating on stainless steel. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40602.