Abstract: Phosphorus promoted presulfided NiMo/Al₂O₃ catalysts were prepared by successive incipient wetness impregnation and characterized by XRD, N₂-physisorption, TPR and HRTEM. The effect of phosphorus on the hydrodesulfurization (HDS) hydrodenitrogenation (HDN) performance of the presulfided NiMo/Al₂O₃ catalyst was investigated. The results indicate that the main active phase is type II MoS₂ or Ni-Mo-S phase because of their weak interaction with the support. The incorporation of phosphorus in the catalyst enhances the dispersion of MoS₂ particles by increasing the stacking number and reducing the slab length. Phosphorus has no influence on the metal-sulfur bonding energies in the Ni-Mo-S phases and bulk MoS₂, but it increases the proportion of Ni-Mo-S phases in the metal sulfides. NiMoP-1.2 catalyst (containing 1.2% phosphorus) exhibits high hydrogenation (HYD) selectivity in the HDS of dibenzothiophene (DBT) and high HDN ratio of quinoline, which can be attributed to its high dispersion of the active phase. The HYD activity in HDS and HDN ratio on NiMoP-1.8 catalyst with excess phosphorus (1.8%) is declined due to the aggregation of MoS₂ particles and the decrease of the catalyst surface area.