IMMUNOTHERAPY plays an important role in cancer prevention and treatment. This study was aimed to investigate the role of milk fermented by Lactobacillus helveticus (L. helveticus) and low dose of gamma radiation (0.25 Gy) as protector and immunotherapy for breast cancer. Female rats were divided into 7 groups, control group, fermented milk with L. helveticus (FM) Group, whole body gamma irradiated group, injected with 17β-estradiol (E2) group, FM and injected with E2 group, gamma irradiation and E2 group and FM then exposed to gamma radiation and injected with E2. Results showed that, E2 caused a reduction in the percentage of cluster of differentiation 4 (CD4) and cluster of differentiation 8 (CD8), an decrease in glutathione (GSH), malonaldehyde (MDA), nitric oxide (NO) levels and glutathione peroxidase (GPx), but increase in catalase (CAT) and superoxide dismutase (SOD) activities as well as an increase in the proliferation marker Ki-67 (Antigen KI-67 also known as Ki-67), with hyperplasia appeared in the histological examinations of mammary tissue epithelium. FM with or without gamma radiation increased CD4 and CD8 count, ameliorated GSH, MDA and NO levels, GPx, CAT and SOD activities and reduced Ki-67 percentage. Histological study showed normal breast tissue. This study demonstrated that FM and gamma radiation (0.25 Gy) induced immunoregulatory and antioxidant capacity in preventing carcinogenic effect of E2 on breast tissue.