A series of copolymers from melamine (MM) and o-toluidine (OT) were synthesized by a chemical oxidative polymerization in an acidic aqueous medium. The dependence of the polymerization yield, particle size, molecular structure, solubility, solvatochromism. and electrical conductivity of the copolymers on the MM/OT comonomer ratio was studied by laser particle size analysis, FT-IR and UV-vis spectroscopies. The results showed that the MM/OT copolymers could be prepared but the MM homopolymer could not be synthesized. It is found that both the polymerization yield and the conductivity significantly decrease with increasing MM content from 0 to 50 mol%, and the solubility in tetrahydrofuran and chloroform exhibits a maximum for a MM content range from 1 to 30 mol%. The diameter of the copolymer particles produced strongly depends on the MM/OT ratio, the polymerization time, and the salt/base forms. The particles become much smaller upon treatment in ammonia because of a change from virgin salt to emeraldine base of the copolymers. The MM/OT (2/98) copolymer base particles exhibit the smallest diameter of 2.097 μ m. The fine particles exhibit interesting solvatochromism and with a wide range of electrical conductivity from 10(-8) to 10(-4) S/cm are potential intensity for a number of different applications. © 2005 Elsevier B.V. All rights reserved.