A novel method, ion diffusion method controlled by ion exchange membrane was reported for the synthesis of Ni(OH)2 nanomaterials in the absence of any template or organic surfactant. The structure and morphology of as-prepared samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), BET specific surface area and pore size distribution analyzer. It can be observed that β-Ni(OH)2 nanoflake-like structure was obtained, and the sheet size, thickness and pore size of as-prepared samples can be controlled by altering reaction time and reaction temperature. The BET specific surface area of Ni(OH)2 nanomaterials obtained by this method can be up to 280.5m2/g at 30°C. The electrochemical supercapacitive properties of Ni(OH)2 nanostructures have been investigated by cyclic voltammetry, chronopotentiometry and electrochemical impedance spectroscopy techniques. All these Ni(OH)2 samples exhibit good capacity for electrochemical supercapacitor in KOH electrolyte. The flake nanostructures synthesized at 50°C for 12h exhibit a highest specific capacitance of 2102Fg−1 at a current density of 20mAcm−2 within the potential range of 0.5V and the Ni(OH)2 sample retains 85.1% of the initial capacitance even after 1000 continuous charge–discharge cycles. The results indicate that ion diffusion method controlled by ion exchange membrane is a useful method for synthesizing inorganic nanomaterials.