Abstract: Thermoelectric conversion technology can convert a large amount of waste heat energy into electric energy for reuse. It is a green energy conversion technology, which can effectively improve energy utilization, and alleviate the energy crisis and environmental pollution caused by the over-exploitation and utilization of coal, oil and other major fossil energy. Therefore, it has been widely concerned by researchers and has become a research hotspot recently. Base on this, one of the more excellent electronic conductive polymers, poly(3, 4-ethylenedioxythiophene) (PEDOT), was used as the research subject, and multiwall carbon nanotubes (MWCNT)/PEDOT composites were synthesized by chemical in situ oxidation synthesis method. X-ray diffraction, raman spectroscopy, transmission electron microscope and positron annihilation lifetime spectroscopy were used to study the microstructure of the composites, the results of which indicate that when the MWCNT content is higher than 24.9wt%, the MWCNTs of MWCNT/PEDOT composites aggregate seriously and are badly dispersed. Thermal and electrical measurements of MWCNT/PEDOT composites show that their electrical conductivity increases sustainably with the MWCNT content increasing. For the pure PEDOT sample, the electrical conductivity is only 7.5 S·m⁻¹, and the electrical conductivity of MWCNT/PEDOT sample is up to 566.59 S·m⁻¹ at MWCNT content of 30.1wt%, the increase is nearly 76 times. Meanwhile, the power factor of the composites increases rapidly from 14.5×10⁻⁴ to 814.3×10⁻⁴ μW·(m·K²)⁻¹ with the increase of 56, which is mainly due to the high conductivity of MWCNT and the π-π interaction between PEDOT molecular chain and MWCNT. With the increase of MWCNT content, the decrease of the first lifetime τ₁ of positron annihilation in materials of PAL test confirms that the interface between MWCNT and PEDOT became smaller and the interfacial interaction between the MWCNT and PEDOT was weakened. As a result, the thermal conductivity of the composite exhibits a bit increase with the addition of MWCNT, but it was far lower than the increase of power factor. Eventually, the thermoelectric figure of merit (Z_T, an index or measure of the thermoelectric properties of a thermoelectric material) value of the MWCNT/PEDOT composites increases from 0.015×10⁻⁴ to 0.45×10⁻⁴, that's a nearly 30-fold increase. In summary, the doped MWCNT of higher conductivity can greatly enhance the thermoelectric properties of electronic conductive polymers of PEDOT.