In a study on l20 ewes belonging to two frocks in Kalubia Governorate, incidence of clinical and subclinical mastitis by using California Mastitis test (C.M.T) was 16.6% and 68.39% respectively. Staphylococcus aureus was the most common pathogen in both clinical (52.5%) and subclinical (24.3%), followed by Streptococcus agalactiae (25.0%) and (21.3%), Streptococcus dysagalactiae (12.5% and 18.2%), Streptococcus uberis (7.5% 17.4%) respectively and Corynebacterium pyogenes was isolated from 2.5% of clinical mastitis only. Drug susceptibility, test was done on isolated strains. Somatic cell count was also performed before and after treatment by using Gentamast intramammary infusion together with gentamycin intramuscular injection for 3 days"