Thermoelectric (TE) performances are systematically investigated for the pellets of poly(3,4-ethylenedioxythio-phene):poly(styrenesulfonate) (PEDOT:PSS) with different organic additives and heating process as organic TE materials. The electrical conductivity, Seebeck coefficient and thermal conductivity versus temperature are determined, respectively. It is found that there is no distinct change for the Seebeck coefficient among each sample with the additions of dimethyl sulfoxide and ethylene glycol. The thermaJ conductivity measured in a wide range of temperature indicates that the PEDOT:PSS pellet have an extremely low value. The highest figure of merit (ZT = 1.75×10-3) is observed at 270K among the PEDOT:PSS pellets.