Sodium oleate (NaOl) is air- and light-sensitive and decomposes during storing. When high-purity NaOl is needed, a fresh sample can be purchased from a chemical company or it can be purified in the laboratory. In this work a procedure of NaOl purification was worked out which consists of dissolution of NaOl in boiling ethyl alcohol (containing 4% water), removal of the insoluble impurities by hot filtration, followed by precipitation of NaOl from the solution at 4 degrees C. The infrared spectroscopy tests revealed that the main decomposition products of NaOl are oleic acid and sodium bicarbonate, apparently formed due to reaction with carbon dioxide and water vapor from the air. In addition to that, an alkaline environment facilitates partial decomposition of oleate leading to the formation of impurities responsible for the yellow color and a characteristic odor of the oleate. The presence of these impurities was detected by liquid-gas chromatography, but their chemical formulas were not determined. The presented procedure of purification removes from the aged sodium oleate its decomposition products but does not eliminate sodium salts of other fatty acids when present in the purified sample.