Abstract: Poly (3,4-ethylenedioxythiophene): poly (styrene sulfonate) (PEDOT:PSS) is employed as a raw material to prepare self-supporting organic thin films with excellent electrochemical properties through post-treatment using sulfuric acid and hydrochloric acid. The morphology, compositions, structure and electrochemical properties of the samples are characterized and analyzed by field emission scanning electron microscope (FESEM), Ultraviolet-visible (UV-Vis) absorption spectra, Raman spectrum, X-ray diffraction (XRD) and electrochemical testing, respectively. The results show that acid treatment can effectively remove the nonconductive PSS in PEDOT:PSS composites and thus greatly improve their conductive properties (around 2~3 orders of magnitude higher than that of the pristine sample). Conductive thin films show excellent electrochemical properties, especially the samples treated with H₂SO₄, which possesses a high specific capacitance (87.3 F/g at a current density of 1 A/g) and good rate capability. In addition to being flexible and self-supporting, the conductive film can be easily peeled from the substrate.