The goal of work was identification of b - casein gene polymorphism in different breeds of cow. The beta - casein constitutes up to 45 % of the casein of bovine milk. The most common forms of beta-casein in dairy cattle breeds are A1 and A2, while B is less common. The b-casein A1 variant was associated with the incidence of diabetes mellitus 1st type, coronary heart disease and autism. The A2 variant reduces serum cholesterol. The material involved 287 cows (Simmental breed – 111 cows, Pinzgau breed – 89 cows, Holstein breed – 87 cows). Bovine genomic DNA was extracted from whole blood by using commercial kit and used in order to estimate b - casein genotypes by means of PCR-RFLP method. In the populations included in the study were detected all three genotypes – homozygote genotype A1A1, heterozygote genotype A1A2 and homozygote genotype A2A2 with frequencies 0.1261, 0.3333 and 0.5405 in Simmental breed; 0.1379, 0.4598 and 0.4023 in Holstein breed, 0.3034, 0.5168 and 0.1798 in Pinzgau breed. In population of Simmental breed and Holstein breed was higher frequency of allele A2 (0.7072 and 0.6322). In opposite, in population of Pinzgau breed was present higher frequency of the allele A1 (0.5618).