The passivation effect of polyaniline (PANI) was utilized to enhance the protection efficiency of styrene-acrylate waterborne coatings against corrosion of carbon steel (CS). Styrene-acrylate emulsion (SACE) based on poly (styrene-co-butyl acrylate) was synthesized via a semi-batch emulsion polymerization while the PANI emulsion (PANE) was prepared by chemical oxidative polymerization of aniline in the micelles of sodium dodecyl benzene sulfonate. The coating formulations (Fs) were prepared by adding PANE to SACE at different weight solid ratios. The viscosity, density, solid content, particle size distribution, the shape of the particles, and stability of the blended emulsions were studied. The properties of the coated-films were evaluated such as hardness, impact resistance, flexibility, adhesion to the steel, glass transition temperature (Tg), and surface morphology. The effect of PANE in enhancing the protection efficiency of SACE film against corrosion of CS was estimated by visual corrosion test, weight loss measurements, and electrochemical Tafel polarization. The results showed an increase in the Tg from 23 oC for pure SACE film up to 36 oC for the film containing the maximum PANI content. SACE film loaded with 0.75% and 1% PANI exhibited the least potential current density of 0.07 and 0.11 µA/cm2, respectively. The formation of a passive layer on the coated-CS was recorded by the shift of corrosion potential for steel to the anodic direction.