Abstract <p>β-casein is a protein consisting of a chain of 224 amino acids, which accounts for approximately 30% of all milk proteins. There are two main alleles of the β-casein gene: A1 and A2. Variant A1 differs from A2 by only one amino acid. Researchers have revealed an association between the carrier of the A2A2 β-casein genotype in cows and the absence of milk allergy in people who consume it as well as the effect of the β-casein gene polymorphism on milk parameters necessary for cheese making. The aim of the study was to study the polymorphism of the β-casein gene in Holstein cows of the Sverdlovsk oblast and its effect on milk productivity. The work was carried out in 2023 on 221 individuals of Holstein cattle belonging to a breeding agricultural organization in the Sverdlovsk oblast. The genotyping of animal DNA by the β-casein gene was carried out using the 7500 Real Time PCR System (Applied Biosystem) device using the 7500 Software V.2.0.1 program. Data on dairy productivity of cows were taken from the IAS SELEX program – Dairy cattle. The frequency of occurrence of the A1A1 genotype was 15.4%, the A1A2 genotype was 42.5% and the A2A2 genotype was 42.1%. The frequency of the A1 allele was 36.7%, and the A2 allele was 63.3%. Milk yield for 305 days of the first lactation of carriers of the A1A1 genotype was 11 697 kg, A1A2 was 11 639 kg, and A2A2 was 11 378 kg. The mass fraction of fat in cows with the A1A1 genotype is 3.65%, A1A2 is 3.73%, and A2A2 is 3.69%. There was no significant difference between the indicators of milk yield and fat mass fraction between carriers of different beta-casein genotypes. The mass fraction of protein in cows with the A2A2 genotype was 3.16%, which is 0.02% (<i>p</i> &lt; 0.05) more carriers of the A1A2 genotype and 0.09% (<i>p</i> &lt; 0.001) more carriers of the A1A1 genotype.</p>