The objective of the present study was to identify the clinical and laboratory findings as well as bacteriological isolates of Clinical mastitis in Holstein- Friesian Dairy cattle. Sixteen cows affected with Staph. aureus (n=10) and E. coli (n=6) acute mastitis were studieded and the results were compared with 12 healthy controls. Anorexia, swelling of the mammary gland, abnormal milk secretion were observed in all cases, while recumbency and sever systemic elevation of rectal temperature, accelerated heart rate and were observed in 5 cases with per-acute form. The chemistry profile revealed hypocalcemia and increased activities of aspartate aminotransferase (AST), creatine kinase (CK) and lactate dehydrogenase (LDH). Necropsy findings were recorded in 5 cases with per-acute form and revealed a grossly swollen gland that contained bloodstained milk. There were extreme vascular engorgement, hemorrhages and necrosis of the parenchyma. Moist gangrene of the overlying skin was also evident. Other postmortem findings included fatty infiltration of the liver, abomasal ulceration and hemorrhagic infarction of the kidney. In conclusion, coliform mastitis and contagious mastitis due to Staph spp. resulting in impact effect in animal health, thus all hygienic control measures should be applied during milk production to prevent such infections.