An optically active copolyaniline, poly(aniline-co-o-toluidine), which forms a different helix structure from that of the corresponding homopolymers was obtained by chemically oxidative polymerization with (1S)-(+)-10-camphorsulfonic acid as the chiral inductor in organic media. Formation of the genuine copolymer rather than a mixture of the corresponding homopolymers was confirmed by cyclic voltammogram, UV/vis, and circular dichroism spectra. The circular dichroism spectra of polyaniline and poly(aniline-co-o-toluidine) at suitable copolymer composition when dissolved in the same organic solvents revealed that their helical windings induced by the same chiral acid are reversed to each other. It is very interesting that the helical conformation of polyaniline can be inverted by inserting o-toluidine units into the polymer main chain. Since the chirality of poly(aniline-co-o-toluidine) depends on the o-toluidine content, this stereo-controlled polymerization of aniline derivatives affords a method to tailor-make electrically conductive materials with specific electrochemical and chiroptical properties. As a proof of concept, extension of this approach to other optically active polymers will be also expected.