A method has been developed for determination of the thermooxidative stability of lubricating oils by substitution of single-stage extraction of mechanical impurities from oxidized oil in a Soxhlet apparatus for stages wherein the oxidized oil is held in a solvent, filtered, and additionally eluted of residue with solvent. The precision indexes of the proposed method meet specifications GOST 11063-77, GOST 23652-79, and GOST 6370-83.