In situ UV-Visible spectroelectrochemical studies on the copolymerization of diaminobenzenesulfonic acid (DABSA) with aniline (ANI), o-toluidine (OT) and N-methyl aniline (NMA) were carried out potentiostatically in aqueous 1.0 M H2SO4 solutions containing the mixture of monomers (DABSA and ANI/OT/NMA) at an optically transparent electrode. Copolymerization studies were performed for different feed ratios of the comonomers. Polymerization of DABSA was also carried out to bring out the differences in the spectral characteristics between homopolymerization and copolymerization. UV-Visible spectra were recorded at various timer intervals during copolymerization and homopolymerization of DABSA. Four absorption bands were noticed for the copolymerization in contrast to the three bands for homopolymerization. The appearance of bands at 672, 633 and 668 nm for copolymerization of DABSA with ANI, OT and NMA, respectively, are attributed to the exitonic transitions associated with these monomer units in the copolymer. The exitonic band of PANI/PANI derivative units that appeared during copolymerization was markedly influenced by the presence of sulfonic acid groups in the copolymer. This was demonstrated by observing its influence in the absence of applied potential and also by following the changes in the band positions through spectroelectrochemical studies on the copolymerization of DABSA with ANI or OT or NMA. The dependences of absorbances on time at the wavelengths corresponding to polaronic and exitonic transitions of the polymers were deduced. The decrease in absorbances of the exitonic band arising from the dedoping caused by sulfonic acid groups in the polymer showed variations in the copolymerization of DABSA with ANI, OT and NMA. The following trend was noticed ANI>NMA>OT.