Magnetic anisotropies and the Curie temperature of a Ni thin film were studied by the magneto-optic Kerr effect. A Ni thin film of thickness of 150 Å was vapor deposited on a Pt(111) surface. Some improvements for detecting the Kerr signal are discussed. From the hysteresis loops of the thin film we found that the in-plane anisotropy is uniaxial. The direction of this uniaxial anisotropy was identified. The Curie temperature of this thin film is 580 K. Magnetization as a function of temperature was studied.