Purpose: This study was conducted to examine the phase transition according to the zirconia surface treatment. Methods: The specimens were divided to four groups. The first group was sintered at $1,500^{circ}C$ and ground; the second group was sintered at $700^{circ}C$, ground, and sintered at $1,500^{circ}C$; the third group was sintered at $1,500^{circ}C$, ground, and $110{mu}m$-sandblasted; and the fourth group was sintered at $1,500^{circ}C$, ground, $110{mu}m$-sandblasted, treated with 9.5% hydrofluoric acid, and ultrasonic cleaner-washed for two minutes. The monoclinic fractions were measured, and the surface was observed via SEM. Results: The monoclinic fraction was $0.13{pm}0.19%$ in the control group Zr1, $1.91{pm}0.15%$ in the experimental group Zr2, $7.71{pm}0.34%$ in Zr3, and $8.39{pm}0.25%$ in Zr4. On the surface, the phase transition hardly occurred in the control group Zr1, but it increasingly occurred in the experimental groups Zr3 and Zr4. Conclusion: The monoclinic fraction was high in the experimental groups Zr3 and Zr4. The phase transition did not occur in the control group, but increasingly occurred in the experimental groups.