The polyaniline (PANI) with different morphologies and particle sizes were successfully prepared through chemical polymerization in 1-ethyl-3-methylimadozolium bromide ([emim][Br]), 1-ethyl-3-methylimadozolium tetrafluoroborate ([emim][BF4]) and deionized water, respectively. The structure and morphology of the resulting PANI were characterized by Fourier transform infrared spectra, X-ray diffraction, and field emission scanning electron microscopy. These samples synthesized in two ionic liquids (ILs) present spherical structure with different sizes (ranging from 100 to 120 nm in [emim][Br] and ranging from 50 to 80 nm in [emim][BF4]). However, the as-prepared PANI using water as solvent presents random stacking nano-cudgel with size of 250-300 nm. The results demonstrate that the imidazolium-based ILs with different anions as template agents play an important role in forming the size and morphology of PANI particles for improving supercapacitor performances, such as low charge transfer resistance, high apparent diffusion coefficient, large redox specific capacity and high-stability. Furthermore, the PANI prepared through [emim][BF4] achieved excellent electrochemical performance with an initial capacity of 625 F g(-1), and retained an effective capacity of 565.8 F g(-1) after 2000 cycles. The results reveal that the chemical polymerization in IL could be a promising new route in preparing specific-size nanoparticles for decreasing transfer resistance and increasing electronic conductivity. (C) 2014 Elsevier Ltd. All rights reserved.