Abstract: Thermoelectric materials can realize direct conversion between heat energy and electric energy, which are safe and environmentally friendly energy materials. With the development of wearable electronic devices, flexible thermoelectric materials attract great interests in recent years. Although conventional inorganic thermoelectric materials have excellent thermoelectric properties, their developments as flexible materials are limited because of their poor brittleness. Poly(3, 4-ethyl-enedioxythiophene): polystyrenesulfonate (PEDOT: PSS) has great potential in the field of flexible thermoelectrics due to its high electrical conductivity, low thermal conductivity and good flexibility. Excellent thermoelectric and mechanical properties can be obtained when choosing appropriate in-organic fillers to mix with PEDOT: PSS. This review focuses on the recent progress of PEDOT: PSS-based flexible thermoelectric materials. We also summarize the effective approaches for improving the thermoelectric performance of PEDOT: PSS-based flexible thermoelectric materials. Finally, we highlight the approaches and challenges for achieving high-performance PEDOT: PSS-based flexible thermoelectric materials.