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, ⍺-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.