Trimetallic Co-Ni-Mo catalysts with different Co and Ni content (Co3Ni0, Co1.8Ni1.2, Co1.5Ni1.5, Co1.2Ni1.8 and Co0Ni3) were studied. Catalysts were characterized by HRTEM, XPS, EXAFS and XANES methods. It was shown that all catalysts contain metals preferentially in the form of sulfide active component with the structure that is similar to Co-Mo-S phase. Co-Mo and Ni-Mo catalysts contain active component in the form of Co-Mo-S and Ni-Mo-S phases respectively. Trimetallic catalysts were shown to contain mixed Ni-Co-Mo-S phases. Catalytic tests showed that the catalyst with 1.8% Co, 1.2% Ni and 10% Mo has the highest activity in hydrotreating of VGO. The highest activity of the catalyst is proposed to be provided by the formation of mixed Ni-Co-Mo-S phase. (C) 2015 Elsevier B.V. All rights reserved.