Kinetic study of the reaction system 4,6-DMDBT + naphthalene + carbazole over NiMo/Al2O3 SiO2 catalysts (0 and 10 wt % of SiO2 in the.support) was carried out using one, two, or three of these components in the reaction mixture. Kinetic equations that best fitted the experimental data were obtained. Then, kinetic parameters were estimated using Powell's minimization. The results show that the catalyst containing silica present higher activity for the transformation of 4,6-DMDBT, naphthalene, and carbazole. It was found that the transformations of 4,6-DMDBT and naphthalene were strongly affected by the presence of carbazole, whereas the hydrodenitrogenation of carbazole in the presence of naphthalene and 4,6-DMDBT was similar to that observed for this compound alone. This behavior was due to the relative values of the adsorption constants of the three components of the reaction mixture.