Directionally solidified alumina-based eutectic in situ composite has complex, irregular and self-similar microstructure composed of two or more phases to form three dimensionally interpenetrating network as "Chinese Script" type structure. In this paper, the fractal analysis is applied to Al2O3/Y3Al5O12 (YAG) eutectic, in situ composite prepared by laser zone remelting in order to quantitatively characterize the microstructure morphology and mechanical property. The fractal dimension of the eutectic microstructure is determined by the box counting technique according to the scanning electron microscope micrograph. The relationships between the fractal dimension and the laser processing parameter, eutectic spacing, and mechanical properties are studied. The results indicate that the eutectic morphology of Al2O3/YAG in situ composite has typical fractal characteristic. The fractal dimension changes from 1.61 to 1.82 when the laser-scanning rate increases from 10 to 400 mu m/s. With the increase of the fractal dimension, the eutectic spacing decreases while the hardness and the fracture toughness all increase. (C) 2007 Elsevier B.V. All rights reserved.