PURPOSE: To produce a lubricant of the subject viscosity grade from a produced isomerized object with a higher yield by subjecting a wax to an isomerization process under the specific conditions on an isomerization catalyst with a low processing gas rate within a specific range.

CONSTITUTION: On an isomerization catalyst (for example, catalyst consisting of platinum on a carrier made of fluorinated γ-alumina), a wax is subjected to an isomerization process at a typical isomerization temp., pressure and specific space velocity (for example, at 270-400°C and 500-3000psi (35.2-210.9kg/cm2) H2, and at a space velocity of 0.1-10V/V/hr) while the processing gas rate remains as low as within 500-5000SCF/bbl H2. A lubricant having a viscosity grade of 5.6-5.9cSt/100°C is recovered from the isomerized product. Through this isomerization process with a low processing gas rate, it is possible to improve the yield of lubricant from isomerized product and lower the wax content of the lubricant fraction of the isomerized product.