The effects of 2-aminobenzenesulfonic acid (orthanilic acid), 3-aminobenzenesulfonic acid (metanilic acid), and 4-aminobenzenesulfonic acid (sulfanilic acid) on the electropreparation and properties of polyaniline (PANI) were investigated in acetonitrile containing 200 mM fluorosulfonic acid. The cyclic voltammetric studies of the products showed characteristics similar to those of conventional PANI in neutral solution, but there was a significant difference between the electrochemical behavior of the polymer films in basic solution. The sulfur-to-nitrogen ratios were found to be about 0.50, which indicated that copolymers were formed. The copolymers were soluble in a basic aqueous solution and in 1-methyl-2-pyrrolidinone and dimethyl sulfoxide solvents. The dry electrical conductivity values of the copolymers were measured. The structure and properties of these conducting copolymers in acetonitrile were elucidated with cyclic voltammetry, Fourier transform infrared spectroscopy, and ultraviolet-visible absorption spectroscopy.