The nanocrystalline zirconia powder with anisotropic shapes was synthesized by hydrothermal treatment of the tetragonal zirconia prepared by aging the zirconium hydroxide precipitate, which was obtained from the reaction between $ZrOCl_2{cdot}8H_2O$ and KOH solutions under the fixed pH of 13.5, at $100^{circ}C$ for 24 h. With increasing the hydrothermal reaction temperature and time, the fraction of tetragonal phase with spherical zirconia decreased, whereas, relatively the fraction of monoclinic phase with spindle-like and rod shape zirconia increased. As increased concentration of the NaOH solution it promoted the particle size to become larger and the crystalline phase to transform tetragonal to monoclinic. However, the specific surface area at the early stage of the reaction increased and subsequently decreased because of grain growth in powder with longer reaction time.