In dairy farms at different localities in Kalubia Governorate, a total of 43 Frisian dairy cows (6-10 years old) were used in this study. Bacterial mastitis was recorded in 36 cows. All affected cattle fed ration contain iron, zinc and copper within that recommended by National Research Council for dairy cattle. The major clinical signs observed on mastitic cows were, general depression, anorexia, fever, ruminal atony, decrease in milk yield marked, changes in the physical characters of milk and signs of inflammation of the affected udder in the form of enlargement, hotness, and pain. Milk samples were taken for bacteriological examination and blood samples were collected for serum preparation and biochemical analysis. According to bacteriological examination, 8 cases were diagnosed as coagulase positive Staphylococcus mastitis, 5 cases as E.coli mastitis, and 23 cases as mixed bacterial mastitis. The biochemical data revealed a significant decrease of serum iron and zinc in all mastitic cow compared with cows treated from bacterial mastitis with suitable antibiotic. On the other hand, serum copper showed no significant changes between before and after treatment of bacterial mastitis.