Description: The aim of the study was to investigate of bacteria that cause subclinical of mastitis in cows of breed Holstein Friesian. The samples were taken in the in Bitola region, North Macedonia for the period from March 2016 to September 2017. Sixteen strains were isolated and identified based on their growth, colony morphology, gram stain, catalase and oxidase activity, using standard protocols. The study found that most common bacteria that cause mastitis are: Staphylococcus aureus, Streptococcus uberis, Streptococcus epidermidis, Streptococcus agalactiae, Streptococcus dysagalactiae, Enterobacter aerogenes and Klebsiela pneumoniae. The obtained findings correspond to the published data in other recent studies