A total of 285 quarter milk samples presented by cow owners and field veterinarians from 137 dairy cow s of 41 herds were examined for mastitis and the following results were obtained. 2. The highest percentage of quarter infected by mastitis was observed in August and other month were low. 3. It was found that 89 quarters (3.22%) were acute mastitis, 791 quarters (67.00%) were chronic mastitis and 5 quarters(1.78%) were mastitis before parturition. 4. The main causative organisms of the mastitis were Staphylococcus spp. (39.63%), Streptococcus spp. (38.22%). 5. The majority of causative organisms were very resistant to penicillin (85.4%) and streptomycin(78.1%). Most of the other drugs were highly effective as inhibitor for the most causative organisms in vitro.