Water-soluble polyaniline poly(acrylic-acid),(PANI-PAA) composites with excellent procssability and electroactivity were prepared by a one-step in situ polymerization. PAA as a matrix not Only improves the solubility of PANT in water but also prevents the formation of macroscopic PANT clusters. The corrosion-inhibition performance of 316 stainless steel (316SS) was evaluated in 0.5 M HCl by electrochemical measurements in the presence of PANI-PAA composites. The results show that PANI-PAA acts as a mixed-type inhibitor, and its inhibition efficiency (Moo) increases with inhibitor concentration. The adsorption of the inhibitor on 316SS surface obeys a Langthuir adsorption isotherm. The PANI-PAA composite with an,optimized concentration of 200 ppm shows marked increase in IE(R)), i.e., 91:68%. The enhanced efficiency is attributed to an insulating interfacial layer formed by the adsorption of PANT PAA,,Which obstructs the,corrosion reaction at the interface.