Abstract: Heavy oil hydrotreating catalysts NiW/CTS were prepared by iso-volumetric impregnation method, where the catalyst support (CTS) was obtained from in-situ growth of TiO₂-SiO₂ oxides covering on the particles of Y zeolites. NiW/CTS catalysts were then modified by surface impregnation of phosphoric acid or co-impregnation of phosphoric acid with metal precursors. The effect of phosphoric acid modification on the physic-chemical properties and hydrotreating performance of the NiW/CTS catalysts were investigated. The results showed that the phosphoric modification causes a decrease of acid amount in NiW/CTS; surface impregnation reduces Lewis acid sites, while co-impregnation enhances the Lewis acid sites. The presence of phosphoric acid in NiW/CTS can weaken the interaction between the support and metal components and improve the dispersion of active metals on the catalyst surface. The co-impregnation method can promote the formation of metal oxide precursor with high hydrogenation activity; therefore, NiW/CTS catalysts modified by phosphoric acid co-impregnation exhibits better performance in hydro-desulfurization, hydro-denitrogenation and hydro-dearomatics.