CoMo-catalysts modified by boron were studied. Boron was added to alumina support by kneading. Supports and catalysts were characterized by nitrogen adsorption, XPS, IR-spectroscopy of adsorbed CO. Catalysts were tested in hydrotreating of straight-run diesel fuel with 5 vol.% catalytic cracking gasoil (initial S content was 2750 ppm). It is found that boron has no significant influence on textural characteristics of catalysts. However, it increases slab length and visualization degree of active component, while stacking number remains unchanged (preferential formation of monolayers). Difference in morphology is caused by changes of Lewis acidity and generation of Bronsted acid sites. It is found that all catalysts with boron provide production of ultra-low sulfur diesel fuels (less than 10 ppm). The catalyst with a boron content of 2 wt.% combines high activity in HDS and HDN. (C) 2016 Elsevier B.V. All rights reserved.