Various Y2O3/ZrO2 samples were fabricated by hot pressing, whereby Y2O3 was mutually dissolved or reacted with ZrO2 as a solid solution or Zr3Y 4O12. Hot-pressed samples were allowed to react with Ti melt at 1700°C for 10 min in argon. Microstructural characterization was conducted using X-ray diffraction and analytical electron microscopy. The Y 2O3/ZrO2 samples became more stable with increasing Y2O3 because Y2O3 was hardly reacted and dissolved with Ti melt. The incorporation of more than 30 vol% Y2O3 could effectively suppress the reactions in the Ti side, where only a very small amount of α-Ti and β'-Ti was found. When ZrO2 was dissolved into Ti on the zirconia side near the original interfaces, Y2O3 reprecipitated in the samples containing 30%-70 vol% Y2O3, because the solubility of Y2O3 in Ti was very low. In the region far from the original interface, α-Zr, Y2O3, and/or residual Zr3Y4O12 were found in the samples containing more than 50 vol% Y2O3 and the amount of α-Zr decreased with increasing Y2O3.