We present a facile strategy, for the first time as the best of our known, to prepare high conducting poly(3,4-ethylenedioxythiophene)/poly(4-styrenesulfonate) (PEDOT:PSS) film with a novel nanoporous morphology directly from a commercial PEDOT:PSS dispersion. Both conducting properties and surface morphology of PEDOT:PSS film can be systematically tunable by simply controlling addition of an ionic liquid, 1,3-dihydroxy-2-methylimidazolium bis(trifluoromethylsulfonyl)-imide (DHIL). The electrical conductivity increases from 0.07 for pristine PEDOT:PSS to 55 S cm?1 after addition of 2 wt% DHIL, with no necessary of any further heat treatment, which is around 800 times increase in the electrical conductivity. On the other hand, the discrete compact PEDOT:PSS film is gradually transformed into the nanoporous film with addition of DHIL. It is considered that such size-tunable porous PEDOT:PSS films with high surface area as well as high conductivity combining solution-processibility show great potential in applications that require high interfacial area, such as flexible electronic components, nextgeneration catalytic, and separation supports.