Developing supercapacitors with simultaneous superior power and energy density for energy-storage devices remains a challenge. In this work, single-phase NiS2 microflowers were synthesized through a hydrothermal process coupled with subsequent sulfidation. The obtained NiS2 microflowers perfectly inherited the flowerlike structure of the precursor, which was composed of nanosheets with firmly integrated nanoparticles. With the benefit of the single-phase crystal structure, suppressed surface oxidation, relatively high apparent conductivity, and unique nano/microstructure, the NiS2 microflowers presented outstanding electrochemical performance in the LiOH electrolyte. Specifically, the NiS2 microflowers exhibited high specific capacities of 813 C g(-1) at 1 A g(-1) and 580 C g(-1) at 20 A g(-1) and retained 93% of its initial capacity after 10,000-time cycling test. Moreover, an optimized NiS2/ / activated carbon (AC) hybrid supercapacitor fabricated with NiS2 microflowers as the positive electrode and AC as the negative electrode operated stably at a large voltage window of 1.8 V. It further delivered a considerable energy density of 39.8 W h kg(-1) at 900 W kg(-1). Impressively, the intriguing nano/microstructure further endowed the almost unabated capacitance after continuous cycling of 10,000 times. This study will definitely promote the design and preparation of high-performance nickel-based sulfides for hybrid supercapacitors.