When sintered cubic $ZrO_2$-10mol%$Y_2O_3$ specimens are heat-treated at 1500 ℃ with MgO or $Y_2O_3$ solute, the boundaries between grains migrate, leaving behind them new solid solutions enriched with the solute oxides. With increasing MgO concentrations, there is an increasing tendency for different segments of the same boundary to move in opposite directions and develop faceted shapes. At high $Y_2O_3$ concentrations, recrystallization occurs at grain interfaces and its growth morphology varies with the solute concentrations : recrystallized grains become fine and advancing interfaces are faceted. Most of these phenomena can be successfully explained by coherency strain energy model already proved as the driving froce for CIIM in metallic systems. On the other hand, when MgO and $Y_2O_3$ are added to the liquid phase sintered ($ZrO_2$-10mol%$Y_2O_3$)-CuO specimen, the interfaces between cubic $ZrO_2Y_2O_3$ grains and surrounding CuO-rich liquid become corrugated, and the boundaries between grains migrate. With increasing the ratio of $Y_2O_3$ to MgO, these tendencies decrease to 0, and again increase. When the instability at the solid-liquid interface and boundary migration don't occur, the coherency strain is nearly 0. This result show definitely that the dominant driving force for the instability and boundary migration in oxide systems is also coherency strain energy as in metallic systems.