According to the method of manufacturing refined oil of the present invention, refined oil which has a viscosity of 20 cst or lower at 135.degree. C., a pour point of 30.degree. C. or lower, an alkali metal content of 1 wt ppm or less, a vanadium content of 10 wt ppm or less and a sulfur content of 0.3 wt % or lower can be prepared, by bringing feed oil into contact with hydrogen in the presence of the demetalizing/desulfurizing catalyst 3 and the hydrogenolysis catalyst 5. This method can decrease the viscosity, pour point and sulfur concentration of the refined oil to sufficiently low levels, and decreases the production cost.