Objective: To extract and separate polysaccharide from Melastoma dodecandrum and to analyze the monosaccharide composition. Method: The polysaccharide was extracted by the water and precipitated by alcohol

and then separated and purified by DEAE-cellulose column chromatography. Water-soluble neutral polysaccharide and acidic polysaccharide were obtained. The monosaccharide composition of the purified polysaccharides was determined by HPLC method with precolumn derivatization. Result: The neutral polysaccharide was consisted of glucose

galactose

mannose

arabinose

and rhamnose

with molar ratio of 123:84:27:19:5

also contained a small amount of xylose. The acidic polysaccharide was consisted of galactose

galacturonic acid

glucose

arabinose

mannose

glucuronic acid

and rhamnose

with molar ratio of 14:10:7:6:4:1:1

also contained a small amount of xylose. Conclusion: To develop an analysis method for extracting polysaccharide from M. dodecandrum and determining it's composition

the method is simple

convenient and feasible.