A novel conducting polymer, poly(aniline-co-p-aminobenzoic acid) (PAABA), was successfully synthesized via electrochemical copolymerization of aniline and p-aminobenzoic acid (p-ABA) in 2 M H2SO4 solution. The results of FTIR and SEM revealed the differences between the obtained copolymer and its two corresponding homopolymers. Compared to polyaniline which has a rather limited useful pH range, PAABA presents excellent redox activity from pH < 1.0 to pH 10.0. The ion exchange properties of the copolymer were also investigated by using electrochemical quartz crystal microbalance (EQCM) and cyclic voltammetry, demonstrating a special anion exchange behavior different from polypyrrole. In other words, the spatial structure of anions instead of the radius of anions studied plays a key role in the anion exchange affinity sequence. (C) 2014 The Electrochemical Society.