The selenium analogue of 3,4-ethylenedioxythiophene (EDOT), 3,4-ethylenedioxyselenophene (EDOS), has been facilely electropolymerized with a low oxidation potential at 0.9 V to poly(3,4-ethylenedioxyselenophene) (PEDOS) films in microemulsion system with deionized water (DW) as solvent, sodium dodecyl benzene sulfonate (SDBS) as surfactant and LiClO4 as supporting electrolyte. The effect of microemulsion on the structure, morphology, electrochemical, and optical properties as well as electrochromic performances of PEDOS films was investigated. PEDOS films displayed satisfactory electroactivity, eminent redox stability with compact morphology. PEDOS films prepared from aqueous microemulsion exhibited the electrochromic blue color conversion from deep (reduced) to light (oxidized), and had ordinary coloration efficiencies (24 cm(2)/C, 20 cm(2)/C, 19 cm(2)/C in microemulsion, BmimPF(6) and ACN, respectively), decent contrast ratios (25% in BmimPF(6)), low switching voltages, and color persistence.