Three-dimensional images of the unidirectionally solidified Al2O3-YAG-ZrO2 eutectic composite were obtained by micro-X-ray tomography. Reconstructed three-dimensional images revealed that the frequency of branching of Al2O3 and YAG phases in an Al2O3-YAG-ZrO2 ternary eutectic specimen was lower than that of the Al2O3 and YAG phases in an Al2O3-YAG binary eutectic specimen and that the domain size of branching of the YAG and Al2O3 phases was approximately twice as high as the lamellar spacing between the two phases. The ZrO2 phase was mainly located in the Al2O3 phase and at the phase boundaries between Al2O3 and YAG, but not in the YAG phase. The branching of the ZrO2 phase occurred More frequently in comparison with the YAG and Al2O3 phases. Chain structures between Al2O3/YAG and Al2O3/ZrO2 were formed due to the frequent branching of the three constituent phases. (C) 2009 Elsevier B.V. All rights reserved.