The objective of the investigations performed was to compare changes in the oxidative stability of two plant oils: soya oil and sunflower oil, occurring when storing them. Both the soya oil and sunflower oil were produced using cold pressure and refining processes. Another aim was to determine the effectiveness of quenching free radicals by systems of native antioxidants contained in the oil samples tested. The samples were thermostated at 60°C, and without light. In order to identify changes, the following parameters were determined: peroxide value, quantity of free radicals (DPPH^•) being scavenged, and tocopherol contents during the oil storage. On the basis of the results obtained, it was stated that the rate of oxidation processes was the highest at 60°C in the cold-pressed sunflower oil; it was significantly lower in the two refined oils, and in the coldpressed soya oil, it was the lowest. The active antioxidant system present in the oils appeared to be the most efficient in quenching free radicals DPPH^• in the refined soya oil. Its effectiveness was lower in all other oils, although its value was comparable (similar). The tocopherol contents decreased while storing oil samples, and the decrease degree was different for individual tocopherol homologues; additionally, it depended on the type of oil.