The properties of the Pt-SAPO-31 catalyst in hydrocarbon feed conversion depending on the catalyst chemical composition and crystallinity has been studied on the laboratory scale. The results of pilot testing of a Pt-SAPO-31 catalyst specimen in hydroisomerization reactions of real diesel fractions are presented. It is shown that the catalyst has high activity and selectivity in feedstock transformation as confirmed by a decrease in the cloud- or freezing point of diesel fuel with a yield of 96-98%. Catalyst life tests have shown high operation stability over more than 800 h without variations in the catalytic activity and the temperature characteristics of the product. Hydrogenation of unsaturated compounds present in the feedstock also results in diesel fuel upgrade.