The effects of boron on the hydrogenation (HYD) of 1-methylnaphthalene (1-MNT), hydrocracking (HC) of diphenylmethane (DPM), and hydrodesulfurization (HDS) of dibenzothiophene (DBT) over sulfided Ni-Mo/gamma-Al2O3-B2O3 catalysts have been studied. The results showed that the HC activity of DPM slightly increases with the increase of B2O3; the HYD activity of 1-MNT and the HDS activity of DBT first increase with increasing amounts of B2O3, upto about 1 mol% of B2O3, and then decrease with increasing amounts of B2O3. The Ni-Mo/gamma-Al2O3-B2O3 catalysts have been characterized by X-ray diffraction (XRD) and NH3 temperature-programmed desorption (TPD). The addition of boron slightly improves the acidity of the acid sites. However, when the loading of B2O3 in gamma-Al2O3 reaches about 14 mol%, B2O3 phase first appears, and its content increases with increasing load of B2O3. In Ni-Mo/gamma-Al2O3-B2O3 catalysts, when the loading of B2O3 reaches 5 mol%, MoO3 phase first appears and its content increases with increasing load of B2O3, indicating the lowering dispersion of the catalysts. Thus, the catalytic hydroprocessing activities of these model compounds over the Ni-Mo/gamma-Al2O3 catalysts may be related to the acidity and metal dispersion of the catalysts.