Poly(3-methylthiophene-co-benzanthrone), a novel copolymer, was successfully achieved by electrochemical oxidation of the monomer mixtures of 3-methylthiophene (3MeT) and benzanthrone in the binary solvent system containing boron trifluoride diethyl etherate and acetonitrile. A series of experiments with different monomer feed ratios were carried out to investigate the influence of monomer feed ratio on the electrochemical copolymerization and the overall properties of the copolymer films. The resulting copolymer possesses the advantages of both polybenzanthrone and poly(3-methylthiophene), such as considerable fluorescence property, good redox activity, high thermal stability, and relatively high electrical conductivity. Ultraviolet-visible, FT-IR, and thermal analysis were used to characterize and investigate the structure and thermal stability of the copolymers. Fluorescence spectroscopic studies revealed that the copolymer dissolved in common organic solvents was a good green or yellow-green light emitter, with a strong emission at 499 nm in doped state and 529 nm in dedoped state.