The influence of various characteristics of NiMo/Al2O3 guard-bed catalysts on their activity in the removal of silicon from the diesel fraction has been studied. It has been shown that an increase in the Ni and Mo content leads to a decrease in the amount of trapped silicon in the samples, thereby enhancing the activity of the catalysts in hydrodesulfurization. It has been found that catalysts with an average pore diameter above 130 have the highest silicon-trapping activity.