A hydrogenation catalyst for a hydrocarbon oil, includes an inorganic porous support composed of at least the oxides of aluminum, phosphorus, and silicon, and supporting at least one active metal selected from the metals of Group 8 of the periodic table, at least one active metal selected from the metals of Group 6 of the periodic table, and phosphorus, the phosphorus chemical shift value of the inorganic support determined by .sup.31P-CPMAS-NMR having the peak within the range of 0 to -20 ppm. The catalyst can achieve an extremely high level of hydrogenation wherein the hydrocarbon is decreased in sulfur content to 10 ppm by mass or less and in nitrogen content to 3 ppm by mass or less.