Impurities are removed from polythiophene by mixing a composition comprising polythiophene, water and an organic liquid at a temperature at which the organic liquid dissolves the polythiophene; allowing an aqueous phase to separate from an organic phase and recovering organic phase; adding water to recovered organic phase and mixing the resulting composition at a temperature at which the organic liquid dissolves the polythiophene; allowing an aqueous phase to separate from an organic phase and recovering organic phase; and allowing polythiophene solid to precipitate from recovered organic phase.