The kinetic study of in-situ copolymerization of aniline with o-and p-methylaniline by ammonium persulfate (APS) has been carded out.UV-vis spectroscopic method was used to investigate the course of copolymerization.Structural characterization was studied by FT-IR spectral analysis.The electronic spectra of the copolymers poly(aniline-co-p-toluidine) and poly(aniline-co-o- toluidine) show blue shift.The shift has been observed in the bands corresponding toπ→π~* transition as well as in the exciton transition.The increase in absorbance recorded during the reaction for different concentration of aniline,o-and p-toluidine at various intervals of time of polymerization reaction indicates a growth in the polymer formation.The resulting first-order rate constant was used to calculate the rate of copolymer formation using the rate equation-d[A]/dt=kc~n. The kinetic study of in-situ copolymerization of aniline with o-and p-methylaniline by ammonium persulfate (APS) has been carded out. UV-vis spectroscopic method was used to investigate the course of copolymerization. Structural characterization was studied by FT-IR spectral analysis. The electronic spectra of the copolymers poly (aniline-co-p-toluidine) and poly (aniline-co-o- toluidine) show blue shift. shift has been observed in the bands corresponding toπ → π ~ * transition as well as in the exciton transition. increase in absorbance recorded during the reaction for different concentration of aniline, o-and p-toluidine at various intervals of time of polymerization reaction indicates a growth in the polymer formation. the result first-order rate constant was used to calculate the rate of copolymer formation using the rate equation-d [A] / dt = kc ~ n.