Abstract: Composite of polyaniline (PANI)-Mn3O4 (PMC) was prepared by chemical oxidative method using aniline as raw material and ammonium persulfate as oxidant in the presence of Mn3O4 nano-particles. Undoped PMC and undoped PANI were prepared by mixing with ammonia solution to remove impurities. The prepared polymers were characterized by XRD and IR techniques. To study the corrosion protection performance of the prepared polymers, PANI and PMC was coated on steel strip respectively, and the coated strips were immersed in 3.5% NaCl solution and 1.0 mol/L HCl solution respectively. Then open circuit potential and polarization curve measurements of the coatings were carried out to compare their corrosion protection performance. Results indicate that strong interactions of Mn3O4 particles and PANI exist, and the crystallization of PANI molecular chain is affected by Mn3O4 particles as well. The corrosion protection properties of coatings containing PANI and PMC are better than that of varnish, the corrosion current (icorr) of coating containing PMC is the smallest, and thus its corrosion protection performance is the best.