Subclinical bovine mastitis is the most prevalent and responsible for the loss of 70% in production, reducing milk secretion by 45%. Clinical mastitis shows clinical signs, in addition to reducing production. The objective of this work was to study bovine mastitis in the literature and conduct research on bacteria in cases of mastitis in four dairy farms in the region of Pelotas -RS -Brazil. In addition to bibliographic research, pathogenic aerobic bacteria were isolated and identified in 94 milk samples with clinical mastitis (n = 12) or subclinical (n = 82) with positive CMT (+ + +). The samples collected and previously identified in test tubes were cultured in blood agar and oven 36°C/24 h, and reading the results performed within 24h to 36°C aerobically. Bacterial growth was observed in 62 (65.9%) samples: 12 (19.4%) clinical mastitis and in 50 (80.6%) subclinical mastitis. After identified biochemical characterization: Coagulase negative Staphylococcus sp. (n = 29), Staphylococcus sp. Coagulase positive (n = 6), Corynebacterium spp. (n = 16), Streptococcus spp. (n = 7), Streptococcus uberis (n = 4). The knowledge and identification of the etiological agent is important for the correct treatment and implementation of mastitis control and prevention methods and for herd monitoring.