The effect of quinoline on the hydrodesulfurization and hydrogenation activities of bi- and trimetallic NiMo(W)/Al2O3 hydrotreating catalysts obtained using Keggin heteropoly acids H4SiMo3W9O40, H4SiMo12O40, and H4SiW12O40 (denoted as SiMo3W9, SiMo12, and SiW12, respectively) and a mixture of two monometallic heteropoly acids (SiMo12 and SiW12) was studied. The catalytic properties were determined in a fixed-bed microreactor in hydrotreating of model feedstock containing dibenzothiophene and naphthalene and of the same feedstock with the addition of quinoline. The trimetallic NiMoW/Al2O3 sample based on the mixed SiMo3W9 heteropoly acid exhibited 1.5 times higher catalytic activity in all the reactions studied compared to its analog prepared from a mixture of SiMo12 and SiW12 heteropoly acids with the same metal ratio. The trimetallic NiMoW/Al2O3 catalyst based on the mixed SiMo3W9 heteropoly acid surpassed in the activity the NiMo/Al2O3 sample and was more resistant to the inhibiting effect of quinoline than its analog prepared from a mixture of the two heteropoly acids. The correlations of the inhibiting effect of quinoline with the morphology of the active phase particles and the content of promoted active sites Ni(Mo)WS in the bi- and trimetallic NiMo(W)/Al2O3 catalysts were found.