Increasing the voltage window of an electrode material is effective for improving the energy density of aqueous symmetric supercapacitors. Herein, a novel aqueous symmetric supercapacitor equipped with a high cell voltage window of 2.6 V was assembled by P-doped TiO2 nanotube arrays on a Ti sheet. The arrays exhibit a wide potential range of about 1.2 V as the cathode, and a stable wide potential range of 1.4 V as the anode was also obtained. These wide potential windows in the cathode and anode render the symmetric supercapacitor with a very large working voltage window reaching 2.6 V, and thus a high volumetric energy density (1.65 mW h cm-3). These results suggest that P-doped TiO2 nanotube arrays can be promising candidates for energy storage devices.