β-Ni(OH)2 flower-like spheres and nanoflakes were synthesized with strong ammonia water as precipitator and nickel nitrate as nickel source by the hydrothermal method. The phase structure and morphologies were analyzed using XRD and SEM. The results showed that under the same conditions of the pH value and the reaction time, the low temperature was propitious to synthesize β-Ni(OH)2 flower-like spheres. High temperature was in favor of the synthesis of β-Ni(OH)2 nanoflakes. Namely, β-Ni(OH)2 flower-like spheres were obtained at 180 °C for 48.0 h with pH=9.0. β-Ni(OH)2 nanoflakes were prepared at 240 °C for 48.0 h with pH=9.0. The formation mechanism was explored through observing influence of the conditions of the hydrothermal method on the morphologies of the samples.