Abstract: Polyaniline nanoparticles were prepared using mixture of ethanol and distilled water as solvent by a chemicaloxidative polymerization. The structure was characterized by using scanning electronic microscopy (SEM) and Fourier transform infrared (FT\|IR) spectroscopy. The electrochemical performance was investigated by cyclic voltammetry, galvanostatic chargedischarge and electrochemical impedance spectroscopy. The relationship between volume fraction of ethanol and the capacitance of PANI nanoparticles was studied. SEM results showed that PANI nanoparticles were 50—100 nm. The electrochemical performance of polyaniline nanopaticles showed that the specific capacitance was up to 492 F/g when current density was 5 mA/cm2 in 1 mol/L H2SO4 solution. The dispersion was better and the capacitance was higher when the volume fraction ethanol was in the lower ratio. The capacitance of polyaniline nanoparticles and dispersibility decreased with the increasing of volume fraction of ethanol.