Effect of surface characteristics of two species of commercial gamma-alumina (alumina-A and alumina-B) on metal-support interaction and hydrodesulfurization (HDS) activity of the corresponding CoMo catalysts was studied systematically. The HDS activity test; were carried out in a continuous flow fixed-bed micro-reactor. Compared with alumina-A, alumina-B with better crystallinity and less hydroxyl groups can partly inhibit inactive cobalt spinel formation and moderate the metal-support interaction, causing a notable increase in the average slab length and stacking number of MoS(2). It stimulates the promoting effect of cobalt on molybdenum and contributes to a noticeable increase in HDS activity. (C) 2009 Elsevier Ltd. All rights reserved.