The objective of the present work was to compare the basic chemical composition of milk from the cows of two breeds, i.e. Polish Holstein-Frisian black white variety and Simental throughout the summer and winter feeding. The studies covered totally 249 milk samples collected from 66 cows Simental and 64 Polish HF black-white variety. The samples were collected twice, that is in summer (June-July) and winter (December-January). In each milk sample the basic chemical composition was determined. Besides, the simple correlation coefficients between the analyzed milk quality indices were evaluated. The comparison of the chemical composition of milk obtained from black-white cows and Simentalers exhibited that Simental cows produce milk of more favourable ratios between the basic indices, i.e. fat and protein. As a result, the protein-fat ratio proves to be higher. That corresponds to the preferred current nutrition tendencies to decrease dietary fat amount for man. The evaluation of correlations between the analyzed milk quality indices showed positive, highly significant correlation coefficients between protein concentration and the content of casein, fat and dry mass as well as between fat content and dry mass. A significant negative dependence, however, was recorded between a fat content and a protein-fat ratio. For the Simental breed, a significant relation between protein content and protein-fat ratio was obtained as well as high dependence between the content of protein and casein. That indicates higher usefulness of these cows` milk for processing, especially for cheese production.