Treatment with exopolymers of Aureobasidium pullulans SM-2001 containing $eta-1,3/1,6-glucan$ inhibited osteoclastogenesis of bone marrow stem cells in a co-culture system with calvariae osteoblastic cells. In addition, the treatment increased mineral deposition in osteoblastic cells. These two observations prompted us to evaluate whether the exopolymers could be used as an anti-osteoporotic agent, and efficacy of the exopolymers to prevent bone loss was compared with alendronate, a bisphosphonate, in ovariectomized mice prone to osteoporosis. Administration of the exopolymers to the ovariectomized mice resulted in improved effects on femur weight and histomorphometric changes of femur such as trabecular bone volume (TBV), trabecular bone thickness (TBT), and cortical bone thickness (CBT). In conclusion, the exopolymers treatment inhibited bone loss from osteoporosis induced by ovariectomy, and the effect was comparable to alendronate administration.