Chronopotentiometry is employed to prepare polyaniline-silver (PANI-Ag) nanocomposite films in water-in-ionic liquid (W/IL) microemulsion and ionic liquid-in-water (IL/W) microemulsion. The resulted nanocomposites are characterized by scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy and X-ray diffraction. It is demonstrated that the PANI-Ag nanocomposite prepared in W/IL microemulsion is nanofibrous and the Ag nanocrystals with 5 nm diameter are dispersed homogeneously, whereas the morphology of the PANI-Ag nanocomposite prepared in IL/W microemulsion exhibits dendritic structure and the diameter of Ag nanocrystals is 50-100 nm. Further. the effects of different microemulsion systems and electrochemical synthesis conditions on the electrochemical properties of the nanocomposite films are studied by cyclic voltammetry and electrochemical impedance spectroscopy. The pure PANI films are also made for comparative purpose. It is found that the special structures of the PANI-Ag nanocomposite result in more excellent electrochemical activity than that of the pure PANI. (C) 2009 Elsevier B.V. All rights reserved.