The studies conducted aimed at the determination of the effect exerted by phytosterols on the oxidation of cholesterol in a model fat. The model fat was commercial lard (I) and the same lard with 10% of phytosterols added (II). The fats were thermally processed at a temperature of 150ºC during 5, 20, 40, and 60 min periods. The quantitative and qualitative determinations of sterols and their oxidation products were performed using a gas chromatograph conjugated with a mass spectrometer (GC-MS). It was found that the content of cholesterol in thermally processed lard samples without any additions and with 10% of phytosterols added decreased with prolonging the time of heating the samples. In the pure lard, the initial content of cholesterol was 55.4 mg/100 g, and it decreased to 44.8 mg/100 g (I) and to 38.2 mg/100 g (II) after the both model samples were heated during a period of 60 min. Along with prolonging the time of thermal processing, the total content of cholesterol oxidation products (COP’s) in lard without the phytosterols added (I) increased from 1.5 mg/100 g in the sample heated during 5 min to 4.1 mg/100 g in the sample processed during 60 min. The total content of cholesterol oxidation products in the lard with 10% of phytosterols added increased at the beginning of the heating and reached a level of 8.7 mg /100 g after 20 min of being processed. After 40 and 60 min of heating, the COP’s content decreased to 5.5 mg /100 g and 2.1 mg/100 g, respectively. The content of 7 ketositosterol strongly fluctuated while the lard with 10% of phytosterols added was heated. While the fat (II) was heated during a period from 5 to 20 min, the content of 7-ketositosterol decreased from 7.5 mg/100 g to 3.7 mg/100 g; then, after the 40 min heating, it drastically increased to 12 mg/100 g, and after the 60 min heating, it reached a level of 6.4 mg/100 g. The addition of phytosterols to the lard causes the formation process of particular cholesterol oxidation products to accelerate. The maximum content of these products in the lard with phytosterols added (II) was twice as high as in the lard without phytosterols added (I).