To provide a hydrodesulfurization catalyst which exhibits high hydrogenation treatment ability to hydrogenation treatment for ordinary pressure residual oil or reduced pressure sesidual oil being heavy hydrocarbon oil with high sulfur content and stably produces fuel oil with low sulfur content for a long period, a pref. method for preparing this hydrodesulfurization catalyst, and a method for performing advantageously hydrodesulfurization treatment of hydrocarbon oil by using this hydrodesulfurization catalyst.

A hydrodesulfurization catalyst which is a catalyst wherein 1-10 wt.% nickel oxide, 5-20 wt.% molydbenum trioxide, 0.5-2.0 wt.% magnesium oxide and 3-5 wt.% phosphorus pentaoxide to the catalyst are carried on a fireproof oxide carrier and relations of 0.1 ≤ magnesium oxide (wt.%)/ phosphorus pentaoxide (wt.%) ≤ 0.5 and 0.06 ≤ magnesium oxide (wt.%)/ molydbenum trioxide (wt.%) ≤ 0.15 exist among carried ratios of magnesium oxide, phosphorus pentaoxide and molydbenum trioxide and a method for hydrogesulfurization of hydrocarbon oil for performing hydrodenation treatment of the hydrocarbon oil by bringing the hydrocarbon oil into contact with the catalyst in the presence of hydrogen, are provided.