Polythiophene films were synthesized by electrolytic polymerization using nitrobenzene as a solvent and tetra-n-butylammonium perchrorate as an electrolyte. We have evaluated thermoelectric properties of Seebeck coefficient, electrical conductivity, hall mobility and career concentration of the films in the in-plane direction. The films showed a tendency that Seebeck coefficient decreased with an increasing electrical conductivity. The figure-of-merit was calculated assuming the thermal conductivity was 0.1W/Km. The figure-of-merit increased with an increasing electrical conductivity up to 1.5×10 -4/K. The electrical conductivity was mainly changed with Hall mobility, which was related to molecular spacing of the mains chains. Variable range hopping was a determining process of carrier conduction. The easiness of carrier conduction between main chain molecules directly affected the figure-of-merit of the polythiophene polymers.