Several series of morphologically controlled MoO3/SiO2 catalysts were prepared, characterized, and tested for hydrodesulfurization(HDS) of dibenzothiophene(DBT) activity. Molybdenum surface loaded with 4.0 atoms Mo/nm(2) was prepared as sintered hexagonal and sintered orthorhombic, as well as a novel "well dispersed hexagonal" phase. Characterization by XRD, Raman, and O2 chemisorption results reveals that the dispersion of MoO3 over silica depends on the final MoO3 phase in the order of: sintered hexagonal < sintered orthorhombic < dispersed hexagonal phase. Temperature programmed reduction(TPR) results show that both bulk and dispersed microcrystalline of MoO3 reduce to MoO2 at 650 ℃ and to Mo metal at 1000 ℃. HDS of DBT was performed in a differential reactor at 30 atm over the temperature range 350-500 ℃. Activity of MoO3/SiO2 toward HDS of DBT is proportional to dispersion.