Mastitis, which is caused by inflammation of the mammary gland, is the most common and costly disease that affects dairy cows around the world. Treatment of mastitis during lactation is not recommended due to the risks of milk contamination with antibiotics in lactating cows. In this research, a plant with the scientific name (Pulegium Mentha) was used for this purpose. In this research, the effect of Oji essential oil on the treatment of subclinical mastitis in Holstein cows was evaluated. For this purpose, 50 Holstein cows with subclinical mastitis with an average age of 4.5 years and in the middle of the lactation stage were selected. The research was conducted in the form of a completely randomized design with two treatments and twenty-five repetitions, which treatments were: 1- control (without injection of Oji essential oil into the breast area) 2- injection of Oji essential oil into the breast area. The results of the present study showed that the injection of Oji essential oil into the mammary gland improved the average amount of milk production, reduced somatic cells, and increased the percentage of protein, fat and lactose in cows' milk (P<0.05). However, there was no significant difference between the Oji treatment and the control in terms of total elimination of intramammary infections. In general, the results of the study show that Oji essential oil can be used in the treatment of subclinical mastitis of cows.