NiO nanopowders and NiO/nickel foam hybrid were synthesized by microwave hydrothermal method. The Ni(OH)₂ was formed at 160 °C for 30 min under microwave irradiation, and  NiO was obtained while the precursor was calcined at 400°C for 120min. The structure and morphology of the NiO nanopowders and NiO/nickel foam hybrid were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM). NiO nanopowders show the morphology of microspheres (diameter is about 3μm), which are composed of porous nanoflakes. NiO/nickel foam hybrid shows a porous nanoflake array structure, the thickness of nanoflakes is 10nm. Electrochemical studies indicate that the maximum specific capacitance of NiO nanopowders is about 85.4F/g at scan rate of 5mV/s, and even 16.8F/g at 50mV/s, while the maximum specific capacitance of NiO/nickel foam hybrid is up to 234.8 F/g at 5mV/s and 90.1F/g at 50mV/s. Electrochemical impedance spectrum (EIS) data show that the solution resistance (Rs) and charge transfer resistance (Rct) of NiO/nickel foam hybrid (1.9Ω and 0.25Ω) are smaller than that of the sample while NiO nanopowders are coated on nickel foam (3.6Ω and 0.3Ω). In conclusion, the ultrathin porous NiO nanoflake arrays on nickel foam with better electrochemical performance and excellent conductivity appear to be a promising electrode material for supercapacitors.