A facile encapsulation of NiO nanoparticles in mesoporous carbon nanospheres (NiO/MCNs) is demonstrated. Silicate-ion groups on nanosilica surface can react with Ni2+ ions to generate nickel silicate in situ around the SiO2 cores. Such hybrids are introduced into polymer nanospheres prepared by extended Stoller strategy, followed by calcination and template removal to fabricate NiO/MCNs. The typical NiO/MCNs have spherical morphology (similar to 280 nm in diameter), uniform mesopores (5.9 nm), high specific surface area (714 m(2) g(-1)), and well-dispersed NiO nanoparticles (7.20 wt.%). Package mesoporosity among the carbon spheres reduces ion diffusion distance, and the mesopores benefit fast ion transportation. Besides, the introduction of NiO nanoparticles not only provides pseudocapacitance, but also increases the graphitization degree of the carbons and improves crystalline structure. As a result, NiO/MCNs as supercapacitor electrodes show a high specific capacitance of 406 F g(-1) at 1.0 A g(-1) in 6 M KOH electrolyte, and it still maintains 315 F g(-1) at a high loading current density of 20.0 A g(-1). Besides, NiO/MCN electrode retains 91.0% of the original capacity at 3.0 A g(-1) after 10,000 cycles, exhibiting outstanding cycle stability. The easy prepared, well-structured, and high-performance NiO/MCNs provide great potential to support advanced energy storage systems. (C) 2016 Elsevier B.V. All rights reserved.