PURPOSE: To improve the contact efficiency of a hydrogen-containing gas, heavy oil and catalyst particles, and to prevent the entrainment of the catalytic particles in the oily or gaseous product taken out of the system, by containing the above components in fluidized state under specific condition.

CONSTITUTION: The feed heavy oil and catalyst particles for hydrogenation treatment are fed to the reactor 4 having the zone 9 to separate the components by the specific gravity difference, and maintained at 250W600°C under a pressure of atmospheric pressure W350kg/cm2. A hydrogen-containing gas is introduced into the reactor 4 through its bottom at a hydrogen/heavy oil ratio of 100W2,000Nm3/Kl. The heavy oil and the catalyst particles are made to contact with each other in fluidized state by the action of the introduced hydrogen-containing gas, and at the same time to contact with the hydrogen gas. A part of the oily component is separated from the heavy oil-catalyst particle suspension in the separation zone 9, and is taken out of the reactor 4 at a space-hour velocity of the liquid of 0.2W10hr-1 to obtain the hydrogenated oily product.