Recently, organic thermoelectric (TE) materials especially conducting polymers have attracted increasing attention. In this work, we successfully synthesized ultrafine poly (3,4-ethylenedioxythiophene) (PEDOT) nanowires (NWs) (similar to 10 nm) by a simple self-assembled micellar soft-template method and then obtain highly flexible free-standing PEDOT NW films by vacuum-assisted filtration. The films are with very high electrical conductivity (similar to 1340 S cm(-1)). After being treated with 6 M H2SO4 and then with 1 M NaOH at room temperature, the film shows an enhanced power factor of 46.51 mu W m(-1)K(-2) (Seebeck coefficient of 25.5 mu V K-1, electrical conductivity of 715.3 S cm(-1)), which increases by 54% compared with that of the pristine film. To the best of our knowledge, it outperforms the TE performance of all reported one dimensional conducting polymer-based films. In addition, the TE performance of the film almost remains unchanged even after being bent for 200 times, indicating excellent flexibility. A flexible TE prototype composed of six strips (7 mm x 30 mm) of the as-prepared PEDOT NW films connected in series shows an output power of 157.2 nW at a temperature difference of 51.6 K. The free-standing PEDOT NW films show promise to a new generation of wearable TE devices. (C) 2018 Elsevier Ltd. All rights reserved.