The fatty acid composition of milk fat during a year was determined by gas chromatography with the use of a 100-m capillary column with high-polar liquid phase. The experimental material were samples of fat isolated with the extraction method from 30% non-pasteurised cream. The study demonstrated that the range of changes in the content of trans isomers of milk fat over a year was significantly higher than that of cis isomers of those acids. The content of C18:1 trans isomers and cis9trans11 C18:2 (CLA) acid was ca. 3-fold higher, whereas that of trans isomers of C18:2 acid – about 2.5-higher in milk fat from summer feeding of the cows as compared to their concentrations in milk fat from winter feeding. The content of cis9trans11 C18:2 acid in milk fat during a year ranged from 0.39 to 1.76% of the total fatty acid composition. The average content of oleic acid in milk fat from the period of summer feeding accounted for 20.63% and was higher by 2.6 percentage units as compared to fat content in the winter feeding. The concentration of linoleic acid in fatty acid composition was almost constant during a year. The contribution of linolenic acid was reported to range from 0.38 to 1.46% and its content of milk fat from the period of summer feeding was twice as much as that of milk fat from the winter feeding period.