In this work, the effect of crystal facets on the catalytic behavior of gamma-Al2O3 was investigated by X-ray diffraction, transmission electron microscopy, temperature -programmed desorption of ethanol, solid-state Al-27 NMR, infrared spectroscopy, and ethanol dehydration reaction. A series of platelet gamma-Al2O3 were synthesized, in which the relative ratio of (100) facets had been systematically increased. Ethylene formation increased with increasing (100) facets, clearly demonstrating the critical role of these facets as active sites for ethanol dehydration on gamma-Al2O3. This systematic approach is helpful for a better understanding of facet-dependent catalytic properties of gamma-Al2O3 that arise from the interaction between the supported metal and the crystal facets.