We report the synthesis of porous spinel-structured binary NiMn2O4 metal oxide nanoparticles and their performance as electrode material for supercapacitors. Spherical NiMn2O4 nanoparticles of similar to 8 nm average diameter have been synthesized using inexpensive and simple sol-get method, and characterized by X-ray diffraction, field emission scanning electron microscopy, X-ray photoelectron spectroscopy, and Fourier transform infrared spectroscopy. The electrodes made of this single phase spinel nanoparticles exhibit superior electrochemical performance with excellent rate capability, offering highest specific capacitance value of 875 F g(-1) at 2.0 mV s(-1) scan rate in 1M Na2SO4 electrolyte solution. Furthermore, an asymmetric supercapacitor is also assembled and possesses a wide operating voltage window of 1.8 V, exhibiting an energy density of 75.01 Wh kg(-1) at a power density of 2250.91 W kg(-1). The results infer this highly porous binary metal oxide nanostructures are promising candidates for high performance energy storage applications.