Background: Although numerous natural or synthetic drugs have been tested for their radioprotective capacity, yet no suitable drug has been introduced for routine clinical use. In this study the radioprotective effect of "a new herbal immunomodulator" commercially known as IMOD, specifically made to decrease the side effects of HIV virus, was investigated on mouse bone marrow cells. Materials and Methods: Female NMRI mice (in a group of five) were exposed to 2 Gy gamma radiation following three days of intravenously injection (IV) of IMOD at various doses. Mice were sacrificed 48 and 72 h after irradiation. Bone marrow was flushed and slides for bone marrow smears were prepared according to standard method. After staining slides in May Grunwald and Giemsa, polychromatic erythrocytes (PCE) and normochromatic erythrocytes (NCE) were scored for presence of micronucleus (MN). Results: The results showed that gamma irradiation increased the frequency of micronuclei dramatically and excreted cytotoxic effect of cell proliferation. Injection of various doses of IMOD before irradiation however, led to a considerable reduction in the frequency of micronuclei in bone marrow erythrocytes as well as cellular toxicity. Conclusion: Results indicated radioprotective capability of IMOD with a dose reduction factor (DRF) of about 2.3 at a dose of 20 mg/kg body weight. The considerably high DRF might be indicative that IMOD besides being an immunomodulator might also posses’ antioxidant property.