Abstract: A microemulsion provides a superior microenvironment for preparing nanoscale materials. A reversed micelle method has been used to synthesize αNi(OH)2 and a w/o type microemulsion method to synthesize βNi(OH)2. The microstructure of Ni(OH)2 nanoparticles has been determined by SAD, XRD and TEM. The diameter of the nanoparticles is shown by XRD and TEM to be 10nm, while SAD reveals that both kinds of nanoparticles consist mainly of polycrystallites. However, some amorphous nickel hydroxide also exists because the surfactant greatly decreases the growth speed of nucleation.