Self-doped polyanilines were electrochemically synthesized in aqueous acid solutions through the copolymerization of aniline (An) and aniline-2,5-disulfonic acid (ADSA) and the polymerization of ADSA alone. The voltammetry of the copolymers shows characteristics similar to those of conventional polyaniline (PAn), and the copolymers exhibit higher electrochemical activity at values of pH higher than about 4. The presence of ADSA inhibits significantly the growth of PAn. When the relative concentration of ADSA approaches unity, no solid film is able to deposit on the electrode surface. However, the polymerization of ADSA results in the formation of water-soluble poly-ADSA. Electric conductivities of poly-ADSA and poly-An-ADSA are in the magnitude of 10-1-10-2 and 10-0-101Scm-1, respectively, lower than that of conventional PAn, 10°-101S cm-1. The conductivity of poly-ADSA is found to show little pH dependence up to at least 9.