Various highly dispersed Mo supported catalysts with various carriers were prepared for deep hydrodesulphurization of diesel. The carriers included a high surface area and large pore volume gamma-Al2O3, two types of meso-microporous composite molecular sieves prepared by incipient-wetness impregnation method. A new mesoporous, MoSiOx catalyst synthesized with in situ composite method was also studied. The hydrodesulphurization experiments were carried out in a micro-reactor over different catalysts including Mo supported series and a commercial catalyst. Spectroscopic techniques (FT-IR and UV-vis DRS) were utilized to determine the structure of MoOx species. The catalyst characterizations of BET, XRD, FT-IR, UV-vis DRS and FTIR pyridine adsorption indicated that the existences of metal active component of Mo in the catalysts were highly dispersed nano MoO3 clusters and the Mo series catalysts had high surface areas and plenty of large pores which were propitious to the diffusions of reactant and product molecules. Cat(NiMo) exhibited the highest B/L acidity ratio and higher total concentration of Bronsted acid sites and Lewis acid sites, and its HDS activity also gave the highest in this study to produce a sulphur-free diesel, which was verified by the sulphur content in products analyzed by GC-MS methods. (c) 2006 Elsevier B.V. All fights reserved.