Abstract: A catalyst for hydrotreating a heavy hydrocarbon oil containing asphaltenes comprises a porous carrier composed of one or more inorganic oxides of at least one element selected from among those of Groups II, III and IV of the Periodic Table, and at least one catalytic metal component composited with the carrier. The metal of the catalytic metal component is selected from among those of Groups VB, VIB, VIII and IB of the Periodic Table. The catalyst contains about 1 to 30% by weight of such catalytic metal component and has the following pore characteristics with regard to its pores having a diameter of 75 .ANG. or more: an average pore diameter APD of about 180 to 500 .ANG., a total pore volume PV, expressed in cc/g, being equal to or greater than a value X ##EQU1## the volume of pores with a diameter of about 180 to 500 .ANG. being at least about 0.2 cc/g, the volume of pores with a diameter of at least 1,500 .ANG. being not greater than about 0.03 cc/g, and a total surface area being at least about 60 m.