Problem statement: The seeds of Nigella sativa Linn. (Ranunculaceae) known as black seed or black cumin, are used in herbal medicine all over the world for the treatment and prevention of a number of diseases and conditions that include asthma, diarrhea and dyslipidaemia. Approach: In this study the effect of intramammary injection of Nigella Sativa Extract (NSE) in paraffin on quarter milk, quality and Somatic Cell Count (SCC) and the shedding pattern of Staphylococcus aureus were investigated. Thirty Holstein cows, naturally infected with S. aureus subclinical mastitis, were subjected to treatment with the NSE at a dose of 10 mL in paraffin (200 mg mL⁻¹) per day for 3 days, or with 10 mL paraffin as control. The injection areas were checked for adverse reactions. The daily milk production was measured before and after treatment. Intramammary injection of NSE caused a remarkable healing. Quarter milk samples were collected for bacteriological analysis and Somatic Cell Counts (SCC). The bacterial count moderately decreased in the treatment group. After the end of the treatment, the numbers of S. aureus-infected quarters and milk SCC tended to decrease in the NSEtreated cows. These clarifications were significantly higher one week post-treatment than pretreatment. Similar changes were not observed in the control group. Results: The results of the present study showed that the NSE has potential as a therapeutic agent for S. aureus infection causing subclinical mastitis of dairy cows and may contribute to the cow's recovery from mastitis. Conclusion: In conclusion, the results indicate that Nigella sativa might act as an antibacterial in vivo in dairy cows