The objective of the study was to determine the effect of thermal processing on the composition of sterols contained in rapeseed oil and in mixtures on its basis. The subject of the research comprised rapeseed oil and rapeseed oil with the addition of: 5 % of phytosterols, 5 % of cholesterol, 1 % of BHT, 1 % of squalene, and 16 % of amaranth oil. The samples analyzed were thermally treated using microwave heating and conventional heating processes at 150 ºC. The analysis of the contents of sterols was performed using a gas chromatograph coupled with a mass spectrometer; prior to the analysis, the samples were saponified and derivatized. It was confirmed that the higher sterol losses occurred during the microwave heating than during the conventional heating at 150 ºC. Among all the rapeseed oil mixtures analyzed, the mixtures of rapeseed oil and the BHT added were characterized by the lowest sterol content loss.