Polythiophenes composed of 3,4-ethylenedioxythiophene (EDOT) and 3-hexylthiophene with different composition ratios of EDOT in the repeat unit of the polymer backbone are synthesized by polycondensation reactions. The optical and electrochemical properties of the polymers are compared with those of poly(3,4-ethylenedioxythiophene) and poly(3-hexylthiophene), and they are found to be well correlated with the EDOT composition ratio. In addition, the charge transport properties of the polymer films, measured using the in situ conductivity technique, are discussed in terms of the EDOT composition ratio, regioregularity, and the doping level.