Mesoporous smectite-type clays containing cobalt species in lattice (MST(Co)) were prepared by a hydrothermal method and examined for hydrodesulfurization (HDS). The MST(Co) catalysts showed higher HDS activities than a commercial alumina-supported cobalt-molybdenum catalyst (Co-Mo/Al2O3). The active structure of MST(Co) was studied by in situ X-ray absorption fine structure and nitrogen adsorption techniques. (C) 2003 Elsevier B.V. All rights reserved.