Abstract: A series of NiMo/γ-Al₂O₃ catalysts with different NiO loadings were prepared and characterized by XRD, BET, ²⁷Al-NMR, Py-IR and HRTEM. The activity of these NiMo/γ-Al₂O₃ catalysts in the hydrodesulphurization (HDS) of dibenzothiophene (DBT) was evaluated in a high pressure micro reactor; the interaction between Ni promoter and γ-Al₂O₃ support as well as its effect on the nanostructure of active MoS₂ phase and HDS performance was then investigated. The results indicate that Ni promoter prefers to interact with the tetra-coordinated unsaturated aluminum sites on the support surface. With the increase of NiO loading, the average number of stacking layers for the MoS₂ clusters in the sulfided NiMo/γ-Al₂O₃ catalysts is increased at the expense of the average length. As the slim MoS₂ clusters are more active for the HDS of DBT, the addition of Ni promoter is then effective to enhance the catalytic activity of NiMo/γ-Al₂O₃ in HDS, but may lead to a slight decrease in the hydrogenation selectivity.