The shape of ZnO grains in liquid $Bi_2O_3$ changes from hexagonal rod to sphere with increasing the temperature, suggesting that the mechanism of the grain growth also changes with temperature. In order to determine the grain growth mechanism with temperature, two kinds of $ZnO-Bi_2O_3$ compacts containing different amount of $Bi_2O_3$ have been sintered at various temperatures. The grain growth rate decreases with increasing the liquid volume at 1400℃. This result shows that the growth of ZnO grains with round shape is controlled by the diffusion of atoms through the liquid. In contrast, faster growth of grains results as increasing the liquid volume at 900℃. This result may imply that the growth of faceted ZnO grains is not controlled by atom diffusion but by the reaction at grain-liquid interface. Neverthless, since the growth rate is affected by the liquid volume, the growth mechanism seems to be not as simple as the classical theory of grain growth in a liquid matrix. Therefore, a further study must be needed to determine conclusively the growth mechanism faceted ZnO grain in $Bi_2O_3$ matrix.
