Vertically aligned conducting polymer nanowire arrays have great potential applications in supercapacitor electrode materials. In this paper, we report a facial one-step template-free approach to synthesize large arrays of vertically aligned polyaniline (PANI) nanowires on various conducting substrates by using a galvanostatic current method. The as-prepared large arrays of PANI nanowires had very narrow diameters and were oriented perpendicular to the substrate, which was a benefit to the ion diffusion when being used as the supercapacitor electrode. The highest specific capacitance of PANI nanowire arrays was measured as 950 F·g−1 and kept as high as 780 F·g−1 at a large charge−discharge current density (40 A·g−1). Furthermore, the capacitances in several different electrolytes, including HClO4, lithium bis(trifluoromethane sulfonyl) (LiTFSI) aqueous solution and nonsolvent electrolyte ionic liquid, were investigated. The results indicated that the orientation of nanostructures could dramatically enhance the electrochemical performance of functional nanomaterials.