Herein, the perfect 3D sponge-like porous structure of Mn2O3 tiny nanosheets grown on Ni(OH)(2)/Mn2O3 nanosheet arrays was successfully manufactured in situ on conductive Ni foam substrate (NiMn@Mn-1 h) by a cost-efficient and facile two-step hydrothermal method. This method included first step to synthesize Ni(OH)(2)/Mn2O3 on Ni foam and second step to regrow Mn2O3 nanosheets on Ni(OH)(2)/Mn2O3 skeletons at a higher temperature. The synergy of Ni(OH)(2)-Mn2O3 and its 3D sponge-like porous morphology that is composed of tiny interconnected radial nanosheets have greatly improved conduction of electron in electrode materials and the contact area of the active materials and electrolyte. Meanwhile, the structure that possesses open channel towards electrolyte also could provide convenient access of electrolyte, promoting release of the intercalation/deintercalation pressure of electrolyte ions. Therefore, the novel sponge-like NiMn@Mn-1 h takes on an outstanding specific capacitance of 2274.4 F g(-1) at a current density of 1 A g(-1). And an impressive cycle stability of 87% at 5A g(-1) over 10,000 cycles is also shown, which mainly benefits from the protection of external Mn2O3 nanosheets prepared by second step hydrothermal method. Further, the assembled NiMn@Mn-1 h//active carbon (AC) quasi-solid-state asymmetric supercapacitor (ASC) also displays a great specific capacitance (117.1 F g(-1) at 1A g(-1)), an excellent cyclic stability (83% after 10,000 cycles) and a high energy density of 41.6 Wh kg(-1). So NiMn@Mn-1 h could be one of the potential materials for application of energy storage devices.