A novel copolymer based on 6-cyanoindole (6CNIn) and 3,4-ethylenedioxythiophene (EDOT) was electrochemically synthesized in acetonitrile containing tetrabutylammonium tetrafluoroborate (TBATFB). The copolymer P(6CNIn-co-EDOT) was characterized by cyclic voltammetry, FT-IR, H-1 NMR, SEM, and spectroelectrochemical analysis. According to the results of FT-IR and H-1 NMR spectra, the electrochemical copolymerization located at C-(2), C-(3) position of 6CNIn. Spectroelectrochemical analysis indicates this copolymer film has distinct electrochromic properties, which can convert between brick-red in the reduced state and sky-blue in the oxidized state. Thus, an electrochromic device (ECD) based on P(6CNIn-co-EDOT) and poly(3,4-ethylenedioxythiophene) was also constructed, which had a color change from dark green in neutral state to dark blue in oxidized state. This ECD showed good optical contrast (30 % at 485 nm, 32 % at 610 nm), high coloration efficiency (216 cm(2) C-1 at 485 nm, 223 cm(2) C-1 at 610 nm), fast response time (0.7 s at 485 nm, 0.9 s at 610 nm), and long-term stability.