Objective To observe the effect of marin algae polysaccharide derivant on the osteoporotic model of the rats. Methods Forty six-month-old female Wistar rats were selected to duplicate the osteoporotic model induced by retinoic acid and performed with marine algae polysaccharide derivant. The rats were randomly divided into two groups: experiment group treated with 10 mg marine algae polysaccharide derivant10mg per day by oral,control group treated with 10 mg glucose per day by oral.The effect of marine algae poly saccharide derivant on osteoporosis were evaluated by morphometry. Results After intake of polysaccharide,the mean trabecular plate density (Tb.N),the mean trabecular plate thickness(Tb.Th),and the percent trabecular area (Tb.Ar%) of t he experiment group, which were treated by polysaccharide were significantly increased more than that of the control group model(P<0.01). Conclusion These results indicate that polysaccharide can increase bone mass and has a therapeutic and preventional effect on the osteoporotic model of the rats induced by retinoic acid.