PURPOSE: To obtain easily a lubricating oil having a viscosity, specific gravity, acid value, etc. approximate to those of a fresh oil by removing a precipitate from a waste oil of an engine oil with a mixed solvent of a hydrocarbon solvent with propyl alcohol, and distilling the liquid component.

CONSTITUTION: A waste oil of an engine oil is mixed with a mixed solvent of (A) a (halogenated) hydrocarbon solvent having a boiling point ≤150°C with (B) propyl alcohol, stirred thoroughly and allowed to stand or centrifuged to remove the precipitate. The mixed solvent is then removed from the resultant liquid component by the distillation to give the aimed lubricating oil. A 4W9C hydrocarbon solvent, petroleum ether and carbon tetrachloride, trichlene, etc. may be cited as the component (A), and isopropyl alcohol is preferred as the component (B). The volume ratio between the waste oil and the mixed solvent is 1:0.3W1:20, preferably 1:0.5W 1:10.

EFFECT: The active component, e.g. an additive, can be maintained.