Background: Lactobacillus kefiri (L. kefiri), found in kefir, is noted for its health benefits, including potential breast cancer prevention. Objectives: This study aimed to assess the apoptotic and therapeutic effects of L. kefiri on breast carcinoma in rats. Methods: Five groups of 10 rats each were used: Group 1 (negative control) had no tumors, group 2 where rats in this group were injected subcutaneously with a single dose of 50 mg/kg b.w. of DMBA (in 2 ml of corn oil) into the mammary gland, allowed to develop tumors over a period of 120 days. In the third group (L. kefiri oral “Group 3"), tumor-bearing rats received 0.4 ml of L. kefiri orally, six times a week for 5 weeks. Lactobacillus injection (Group 4) where tumor-bearing rats received 0.1 ml of L. kefiri solution via intraperitoneal injection twice a week for 5 weeks. Finally, the L. kefiri mix group (Group 5) where tumor-bearing rats received L. kefiri solution through duo ways: orally with 0.4 ml six times per week and intraperitoneally with 0.1 ml per tumor twice a week for five weeks.  Results: DMBA reduced TNFR1, cytochrome c, TRADD, and Bax levels, while increasing Bcl-2 level. L. kefiri reversed these effects, promoting apoptosis in cancer cells. It also improved liver and kidney function markers, reduced oxidative stress and enhanced immunity as shown by better antioxidant levels and lower malondialdehyde.                        Conclusion: L. kefiri showed promise as a natural agent against breast cancer, warranting further research to determine its mechanisms and optimal application for human health.