Several series of morphologically controlled MoO₃/SiO₂ catalysts were prepared, characterized, and tested for hydrodesulfurization (HDS) of dibenzothiophene (DBT) activity. Molybdenum surface loading of 0.2 to 4.0 atoms Mo/nm² were prepared as sintered hexagonal and sintered orthorhombic, as well as a novel "well dispersed hexagonal" phase. Amounts of MoO₃ crystal over silica surface was verified by TGA. Characterization by XRD and Raman 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. Surface area of sample is independent of MoO₃ crystal dispersion. Temperature programmed reduction (TPR) results show that both bulk and dispersed microcrystalline of MoO₃ over SiO₂ surface reduce to Mo metal by 2 step reduction. Hydrodesulfurization (HDS) of dibenzothiophene (DBT) was performed in a differential reactor at 30 attn over the temperature range from 350 to 500℃. Activity of MoO₃/SiO₂ toward HDS of DBT is proportional to dispersion.