A series of Al2O3-ZrO2 Composite Supported NiMo catalysts with various ZrO2 contents were prepared. Several techniques including XRD, SEM, N-2 physisorption, H-2-TPR, and UV-vis DRS were used for typical physico-chemical properties characterization of the ZrO2-Al2O3 composite supports and their NiMo/ZrO2-Al2O3 catalysts. The test results showed that the composite supports prepared by the chemical precipitation method existed as amorphous phase in the samples with insufficient contents of ZrO2, and the incorporation of ZrO2 into supports provided a better dispersion of NiMo species, which made their reductions become easier. The pyridine-adsorbed FT-IR results indicated that the Lewis acid sites of catalysts increased significantly by the introduction of ZrO2 into the supports. The activities of these catalysts for diesel oil hydrodesulfurization (HDS) and hydrodenitrogenation (HDN) were evaluated in a high pressure micro-reactor system. The results showed that the ZrO2-Al2O3-supported NiMo catalysts with suitable ZrO2 contents exhibited much higher catalytic activities than that of Al2O3-supported one, and when the ZrO2 contents were 15% and 5%, the NiMo/Al2O3-ZrO2 catalysts presented the highest HDS and HDN activities, respectively. (C) 2009 Elsevier B.V. All rights reserved