Polyaniline-intercalated layered manganese oxide (PANI-MnO2) nanocomposite was synthesized via exchange reaction of polyaniline (PANI) with n-octadecyltrimethylammonium-intercalated manganese oxide in N-methyl-2-pyrrolidone solvent. The PANI-MnO2 nanocomposite was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) spectroscopy, and so on. XRD analysis showed that the basal spacing was 1.47nm, corresponding to the benzene rings of PANI were arranged in a zigzag conformation and located perpendicular to the inorganic layers. The CN stretching vibration (ν CN) which appeared with PANI at 1293cm−1 shifted to 1306cm−1 for PANI-MnO2 nanocomposite, indicating the existence of interactions between intercalated PANI and manganese oxide layers. The XPS results showed that PANI was still in the conductive form after inserting the polymer into layered manganese oxide. The electrochemical properties as electrode materials for electrochemical capacitors were examined by cyclic voltammetry and galvanostatic charge/discharge test in 0.1M Na2SO4 solution. The maximum specific capacitance of 330Fg−1 was obtained from galvanostatic charge/discharge at a constant current density of 1Ag−1. The specific capacitance of PANI-MnO2 nanocomposite had improvement values of 76 and 59% compared to those of PANI (187Fg−1) and manganese oxide (208Fg−1) components, respectively, which was due to synergic effects from each pristine component.