An Al2O3/ Y3Al5O12 eutectic ceramic was prepared with a c- axis sapphire seed by an optical floating zone furnace. The crystallographic relationships in the initial and the steady growth sections of the as- grown eutectic ceramic were investigated by electron backscattering diffraction and transmission electron microscopy. The corresponding results were: < 111 > {101} Y3Al5O12 || < 0001 > {11 - 20} Al2O3 and < 110 > {2 - 11} Y3Al5O12 || < 1 - 100 > {0001} Al2O3, respectively. The steady orientation of the latter one shows smaller planar disregistry. Interfacial strain played the decisive role in affecting the solidification behavior of the Al2O3/ Y3Al5O12 eutectic ceramic. The stability of interfaces with minimum interfacial strain and better ionic charge balance in irregular microstructure prevail upon the constraint of the seed. These results might cast light for the interfacial design of the Al2O3/ Y3Al5O12 binary eutectic ceramic.