Abstract: A catalyst composition for converting hydrocarbons in a hydrotreatment process (hydrodesulfurization and/or hydrodenitrogenization) and simultaneously cracking them, containing an alumina-silica-alumina carrier built up from alumina and silica-alumina, on which hydrogenation metals, such as molybdenum, nickel, and/or cobalt, have been provided and which also contains a catalytically active amount of boron, generally in the range of 1 to 20 wt. %. The invention also relates to a process for the preparation of such a catalyst, with boron being provided ahead of the Group VIII component. The carrier material used may be made up of mixtures of alumina and amorphous silica-alumina or of mixtures of alumina and silica-coated alumina. The catalyst composition is highly suitable for converting vacuum gas oil into middle distillate oils by hydrotreating.