The nanostructured electrode material with high surface area, good porous texture and appropriate pore-size distribution are facilitating more active sites for accumulation of ions and a large rate of ionic diffusion. Here, the mesoporous Ni3S4 nanostructures were prepared through a one-pot hydrothermal method. Annealing temperature which is known to affect the structural, morphological and electrochemical properties of the nanostructure has been optimized. Mesoporous Ni3S4 nanoflakes show a high surface area of 73 m(2) g(-1) at an annealing temperature of 200 degrees C (N2). This porous nanostructure exhibits a high specific capacitance of 1184 +/- 71 to 548 +/- 9 F g(-1) at realistic specific currents of 5 to 40 A g(-1). The symmetric two-electrode system (N2//N2) made up of mesoporous nanoflakes delivers a maximum energy density of 9 Wh kg(-1) at 2 A g(-1) and maximum power density of 4.6 kW kg(-1) at 40 A g(-1). It retains 72% of initial capacitance after 5000 repeated cycling process. In addition, we have used two such symmetric devices to power a red LED. It demonstrates the intrinsic capability of porous Ni3S4 nanoflakes annealed at 200 degrees C to offer enhanced electrochemical performance and further appear to be a promising electrode material for real-life supercapacitors.