The effect of the introduction of P2O5 into Ni-Mo/Al2O3 catalysts on their activity in the hydrotreating of vacuum gas oil has been studied. As the support, gamma-Al2O3 prepared from aluminum hydroxide AlOOH powder of the TH-100 brand (Sasol) has been used. The catalytic properties of the catalysts obtained have been examined in the hydrotreating of vacuum gas oil in a continuous-flow unit under hydrogen pressure. The amounts of sulfur and polycyclic aromatic hydrocarbons, the hydrocarbon group composition, and the carbon residue of the feedstock and the hydrotreating product have been determined. The catalysts after testing have been studied using differential thermal analysis in combination with thermogravimetry (DTA-TGA); the influence of the amount of the modifier on the catalytic activity and coking of the catalysts has been shown.