A nano nickel oxide coated graphene/polyaniline (NiO-GNS/PANI) nanostructure is designed and synthesized as electrode material for flexible supercapacitor application via hydrothermal and in situ chemical oxidative polymerization methods. It is found that this nanostructure exhibits outstanding electrochemical performances, such as high specific capacitance (1409 F g(-1) at 1.0 A g(-1)) and good cycling stability (92% capacity retention after 2500 cycles at 1.0 A g(-1)). The enhanced electrochemical performance of this ternary composite is due to high surface area, low internal resistance, reduction of diffusion length and synergistic effect between individual constituents. A flexible thin-film supercapacitor is fabricated using NiO-GNS/PANI, which presents excellent electrochemical stability at different angles (0-90 degrees) and long cycle life (86% capacitance retention after 1000 bending tests). Such a flexible film is a promising electrode material for application in flexible supercapacitors. (C) 2016 Elsevier Ltd. All rights reserved.