We investigated the characteristics of hot-pressed pure yttria ceramics, and annealed them in an oxidation atmosphere. Regardless of the heat treatment in the oxidation atmosphere, XRD analysis showed that all the samples had a $Y_2O_3$ phase without structural change. Even though the color variation of the hot-pressed $Y_2O_3$ ceramics was due to the sintering temperatures, the oxidation process turned the color of the $Y_2O_3$ ceramics into white. The color change during oxidation treatment appears to be related to oxygen defects. In addition, oxygen defects also affected the weight change and microstructure of the $Y_2O_3$ ceramics. The $Y_2O_3$ ceramic sintered at $1600^{circ}C$ had a $5.03g/cm^3$ density, which is close to the theoretical density of $Y_2O_3$. As the sintering temperature increased, small homogeneous grains grew to large grains which affected the Vickers hardness. $Y_2O_3$ ceramics hot-pressed at $1600^{circ}C$ and annealed at $1200^{circ}C$ had a flexural strength of 140MPa.