Currently, mastitis of infectious etiology remains a significant problem for dairy farming, which are widespread and cause enormous economic damage. The frequency of occurrence of mastitis by months during the year varies from 1.9 to 7.7 %. In general, 33.1 % of cows get sick by mastitis during the year. Staphylococcus aureus, Streptococcus zooepidemicus, Streptococcus dysgalactiae are isolated from the milk of cows cows suffering from mastitis. Streptococci have such virulence factors as a capsule, fimbriae (M-proteins), toxins, enzymes. Staphylococci are able to form a microcapsule and biofilm, adhesins, enzymes, toxins, etc. Prevention of mastitis should consist of a complex of veterinary, sanitary and zoohygienic measures. As part of a study on the specific prevention of mastitis in dairy cows, an associated strepto-staphylococcal vaccine was tested. According to serological studies in indirect hemagglutination reaction and diffuse precipitation reaction, after double immunization of cows the suffcient titers of antibodies to staphylococcal and streptococcal antigens were developed (diagnostic titer is 1:40) to create specific immunity. The maximum increase in titer antibodies is noted by the 28th and 48th days of the study, respectively. Serum bactericidal activity and serum lysozyme activity indicators also acquired initial values by day 48. The results obtained provide grounds for further study and use of an experimental vaccine for cows.