Osteoporosis is a disease of aging associated with bone loss that often occurs without symptoms until microarchitectural deterioration becomes so significant that bone fracture occurs. The effective microorganism-X (EM-X) is an antioxidant beverage derived from ferment of unpolished rice, sea weeds and papaya with effective microorganisms of lactic acid bacteria, yeast and photosynthetic bacteria (containing minerals, a-tocopherol, lycopene, ubiquinone, saponin and flavonoids). The levels of serum estradiol (E2) and the bone density of the middle and epiphysis of femurs were assessed in order to determine the effect of EM-X on osteoporosis in ovariectomized rat (an animal model of postmenopausal osteoporosis). EM-X (1ml/rat/day) was initially administrated by gavage to rats which were then allowed to consume 10% (v/v) EM-X in water freely for 3 months. There was no statistical significance of E2 level between sham operation group and control group, indicating that sham operation did not affect E2 level. However, the E2 levels in the ovariectomized rats tended to increase after treatment of EM-X for 3 months. The bone density of the middle and epiphysis of femur in both sham operation and ovariectomy group decreased with time. Rats receiving EM-X for 3 months after sham operation or ovariectomy had increased bone density of the middle of femur that was statistically significant (P<0.01 and P<0.05). The bone density of the epiphysis of femur in both sham operation and ovariectomy group were significantly increased, an outcome highly suggestive of the beneficial effects of EM-X on bone density of the middle and the epiphysis of femur in the rats with or without ovariectomy.