PURPOSE: To recover a solvent at a low temp. by subjecting a mixture contg. the solvent and oil to a reverse osmosis treatment.

CONSTITUTION: The mixture contg. the 3-6C aliphat. hydrocarbon solvent (e.g. propane, butane) and the oil, for example, the mixture composed of the aliphat. dewaxing solvent and dewaxing oil, is brought into contact with one side of a reverse osmosis membrane having a pore diameter of ≤1.0 μm, more preferably 0.01 to 0.001 μm at a temp. between -10°C and the cloud point of the oil described above under an apparent pressure difference of 3.5 to 105 kg/cm2, more particularly 28 to 70 kg/cm2 to allow the selectively penetrate the membrane, by which the solvent is recovered. The reverse osmosis membrane is preferably a polyimide membrane, more particularly preferably an asymmetric polyimide membrane. The recovering method is useful for a low-energy integration system in dewaxing of the oil.