Electroactive poly(4-methyl carbazole-3-carboxylic acid) (PMCCA) film was formed on Pt electrode surface by oxidative electropolymerization of a new carbazole derivative. The structure of the soluble polymer was elucidated by nuclear magnetic resonance (H-1 and C-13 NMR) and Fourier transform infrared (FTIR) spectroscopy. The average molecular weight has been determined by gel permeation chromatography (GPC) to be M (n) = 51,000 for the electrochemically synthesized polymer. Characterizations of the resulting polymer were performed by cyclic voltammetry, dry conductivity measurement, scanning electron microscopy, and UV-vis spectroscopy. Spectroelectrochemical studies indicated that PMCCA films revealed a green color in the oxidized state and a high transmittance in the neutral state. The conductivities of PMCCA are in the range of 10(-5)-10(-4) S cm(-1).