Nickel hydroxide nanowires were prepared by hydrothermal method. The produ cts were characterized by powder X-ray diffraction(XRD) and transmission electro n microscopy(TEM). The results show that the morphology of nickel hydroxide nano wire is mainly straight. The diameters of the nanowires are about 20~30 nm and t he lengths reach several micronmeters. The effects of hydrothermal reaction time and filling factor on the morphologies and structure of the products were studi ed. The formation mechanism for nickel hydroxide nanowires is also discussed.