The electrochemical synthesis of conducting polymers (polythiophene and polypyrrole) within cylindrical pores in membranes as a template was carried out in a supercritical fluid such as supercritical trifluoromethane (scCHF3). The use of the special properties of the fluid such as higher diffusivility and lower viscosity enabled the effective monomer transport into the nanoporous template and the nanoprecise filling with the polymers. The height of the polymer nanowires electropolymerized in scCHF3 was appreciably uniform compared with that deposited in a liquid medium like an acetonitrile solution and the height was found to be correlated exactly with the deposition time. The diffusivility of media used for the electrodeposition also affected on strength and structures of the cylindrical-shaped polymer materials obtained by dissolving the membranes in NaOH aqueous solution. The highly aligned polymer nanowire arrays prepared by the present method showed better electrochemical behaviors compared to nanowires obtained in the acetonitrile electrolytic solution.