Interesterification is one of the methods for modifying fat properties. With this method, it is possible to make products of a predetermined structure of lipids. The interesterification process may affect oxidation resistance, thus, the stability of a fat product. A Rancimat test is a method that is both the most popular and the most frequently applied to investigate the stability of fats; this Rancimat test was applied to the investigation as presented in this paper. It was studied in what manner the type of catalyst used during the process, and the conditions of reaction affected the oxidation of interesterified blends made of rapeseed oil and milkfat. Blends of rapeseed oil and milkfat, their composition by weight being 1:1, constituted the material for the investigation. The aforesaid blends were chemically interesterified in the presence of sodium methoxide as catalyst, and, then, enzymatically interesterified using enzymatic preparations with lipases of various specificity. The chemical interesterification was accomplished at a temperature of 90°C, during a period of 1.5 hours, and the enzymatic interesterification: at a temperature of 70°C, during 8 hours. The results of the investigation performed prove that the interesterification process has an impact on reducing the antioxidant stability of fats. Triacyloglicerols isolated from the interesterification products were characterized by the lowest antioxidant stability.