To provide a hydrogenation process for a gas oil fraction wherein a high-quality gas oil having a low sulfur content and a low polycyclics aromatics content is efficiently prepared.

In the presence of a hydrogenation catalyst, a gas oil fraction is mixed with a hydrocarbon oil, which has a higher boiling point than the gas oil fraction, as a diluent and hydrogenated, or a hydrogenated product is vapor-liquid separated to obtain a vapor-phase fluid which is further hydrogenation modified to prepare a gas oil having a sulfur content of 50 wt.ppm or smaller and a polycyclic aromatics content of 1 vol.% or smaller. The hydrogenation treatment is chosen from hydrodenitrification, hydrogenolysis, nuclear hydrogenation and hydrodesulfurization, and the hydrogenation catalyst is chosen from catalysts wherein metals belonging to group 6, 8, 9 or 10 of the periodic table is carried on amorphous inorganic oxide supports and zeolite-containing catalysts.