A mesoporous aluminosilicate molecular sieve with MCM-41 type structure was synthesized using aluminum isopropoxide as the Al source. Supported Co-Mo/MCM-41 catalysts were prepared by co-impregnation of Co(NO 3 ) 2 .6H 2 O and (NH 4 ) 6 Mo 7 O 2 4 followed by calcination and sulfidation. For comparison, conventional Al 2 O 3 -supported sulfided Co-Mo catalysts were also prepared using the same procedure. These two types of catalysts were examined at two different metal loading levels in hydrodesulfurization of a model fuel containing 3.5wt% sulfur as dibenzothiophene in n-tridecane. At 350-375 o C under higher H 2 pressure (6.9MPa), sulfided Co-Mo/MCM-41 catalysts show higher hydrogenation and hydrocracking activities at both normal and high metal loading levels, whereas Co-Mo/Al 2 O 3 catalysts show higher selectivity to desulfurization. Co-Mo/MCM-41 catalyst at high metal loading level is substantially more active than the Co-Mo/Al 2 O 3 catalysts.