In the study, seasonal changes in the composition of triacylglycerols (TAG) in milk fat from Simmental cows were analyzed and compared with the composition of TAG in the fat of aggregated milk from cows in the Mazovia region (mainly from cows of the Polish Holstein-Frisian breed, Black and White variety). Both the experimental herd (27 cows) and the cows in the region analyzed were fed using a traditional system based on silage and hay in winter, and supplemented by pasture feeding in summer. The analysis of the TAG composition using a gas chromatography made it possible to detect 16 TAG classes with the following quantitatively prevailing groups: CN36, CN38, CN40, CN48, CN50, CN52. The Simmental cows’ milk was characterized by the highest content of CN38 (12.50 %) and the lowest content of CN26 (0.35 %). Similarly, in the aggregated milk collected in the region, the content of the CN38 group (12.48 %) was determined the highest, and that of CN24 (0.24 %) the lowest. As regards the contents of TAG classes: CN24, CN26, CN28, CN30, CN32, CN34, CN36, CN50, and CN52 in milk, statistically significant differences (p < 0.05) were found between the milk from Simmental breed cows and the aggregated regional milk. Regarding the nutritional significance of TAG composition in milk, emphasized should be the higher percent content of TAG (CN26-34) containing short chain saturated fatty acids in milk from Simmental cows compared to samples of milk aggregated in the Mazovia region, and the lower percent content of TAG (CN46-54) therein containing mainly long chain saturated fatty acids.