Experimental allergic encephalomyelitis (EAE) is considered as the murine model of multiple sclerosis. Daidzein a phytostrogenic compound of soy is known to impose immunomodulatory and antioxidative effects. We conducted this study to assess the potential protective and therapeutic effects of daidzein on allergic encephalomyelitis.C57BL/6 mice were induced with allergic encephalomyelitis using myelin oligodendrocyte glycoprotein (35-55) and received daidzein or dimethyl sulfoxide as the vehicle control. To assess the protective effect of daidzein, the mice were administered with 20 mg/kg of daidzein from 21 days prior to 21 days post EAE induction on a daily basis. To evaluate the therapeutic effect of daidzein, mice were fed with 300 mg/kg daidzein after the appearance of the first clinical signs for 10 days. One day after the last gavage, the mice were sacrificed. Spleen and brain were removed for further histological and immunological analysis.Feeding mice with low dose of daidzein prior to disease induction did not affect disease severity. However, treating with high dose of daidzein after the onset of the disease reduced interferon-3 and interleukin-12 secretion, enhanced interleukin-10 production, suppressed lymphocyte proliferation, and decreased cytotoxicity as judged by lactate dehydrogenase release.In conclusion, daidzein reduced the extent of demyelination and disease severity. Chronic oral therapy with low dose of daidzein did not prevent experimental autoimmune encephalomyelitis. However, high doses of daidzein could prohibit disease exacerbation.