A catalyst for hydrotreating of a gas oil which comprises an alumina-containing inorganic oxide carrier and, carried thereon, 0.1 to 10 mass % of platinum, 0.1 to 20 mass % of palladium and 0.05 to 1.2 mass % of a halogen, characterized in that the crystalline alumina contained in the above alumina has a crystallite diameter of 20 to 40 ANGSTROM ; a method for hydrotreating of a gas oil which comprises carrying out a catalytic reaction of gas oil in the presence of said catalyst; and a method for hydrotreating of a gas oil which comprises a first desulfurization process of carrying out a catalytic reaction of a straight-run gas oil having a boiling range of 160 to 400 DEG C in the presence of a catalyst comprising an inorganic carrier and, carried thereon, 10 to 25 mass % of at least one metal selected from those belonging to 6a Group of the periodic Table and 0.1 to 6 mass % of at least one metal selected from those belonging to 8 Group of the periodic Table, to thereby produce an oil having a content of sulfur compounds of 0.2 mass % or less, and a second desulfurization process of carrying out a catalytic reaction in the presence of a catalyst comprising an alumina-containing inorganic oxide carrier and, carried thereon, 0.1 to 10 mass % of platinum, 0.1 to 20 mass % of palladium and 0.05 to 1.2 mass % of a halogen.