Novel electrochromic copolymers from o-phenylenediamine (oPD) with aniline (ANi) were facilely synthesized by a chemical oxidative polymerization. The synthesis, structure, and properties of the copolymers were systematically studied by changing oPD content and polymerization temperature. The dependence of the polymerization yield at 70 degrees C on the oPD content is quite different from that at 17 degrees C, indicating that the copolymerization between the oPD and ANi comonomers varies significantly with polymerization temperature, whereas the conductivity and solubility of the copolymers obtained at 17 and 70 degrees C demonstrate similar dependency of the oPD content. The reactivity ratios, r(oPD) and r(ANi), of oPD and ANi were found to be 9.70 and 2.74, respectively, implying a stronger homopolymerization tendency than copolymerization between them. The copolymers exhibit stronger formability and uniformity of the film, much higher electroactivity, and better tricolor electrochromism than oPD and ANi homopolymers. The copolymer film, containing 50 mol % oPD unit is red at -0.5 to 0 V vs SCE, turns to green at 0 to +0.6 V vs SCE, and blue at +0.6 to +1.35 V vs SCE. Possible assignments of the macromolecular structures of the copolymers in different potential ranges are proposed. The difficulty of synthesizing electrochromic oPD/ANi copolymers could be overcome to some extent by the oxidative polymerization at 70 degrees C. Particularly, the copolymer has an uncommon combination of strong film formability, high electroactivity, and unique tricolor electrochromism, which could not be achieved by both homopolymers themselves.