A series of catalyst with Mo loading from 2 to 14 wt.% on MgO-Al2O3 mixed oxide support was prepared by incipient wetness impregnation method. Pure MgO and Al2O3 were prepared by using Mg(NO3)(2).6H(2)O and Al(NO3)(3).9H(2)O salt solutions and urea as hydrolyzing agent. MgO-Al2O3 (1:1) mixed oxide was prepared by co-precipitation of appropriate quantities of magnesium nitrate and aluminium nitrate salts. BET surface area, pore volume, pore size distribution, TPR, acidity and acid strength distributions of catalysts and supports were measured. MgO-Al2O3 (1:1) mixed oxide showed a biomodal pore size distribution. LTOC and TPR results show that an optimum 8% Mo on MgO-Al2O3 is sufficient to form MoO3 monolayer. TPR technique can also be used as a vital tool to determine the monolayer coverage. HDS activity has been correlated with LTOC. Introduction of basic MgO in the lattice of Al2O3 moderates the strong acidity in MgO-Al2O3. Impregnation of acidic moO(3) species further enhances the acidity favorable for HYC. (C) 2004 Published by Elsevier B.V.