Objective:To separate and purify the immunoactive polysaccharide RTPS- I from Trichosanthis Radix and study the physicochemical properties and preliminary structure. Methods:The crude polysaccharides were extracted by water, and then precipita-ted by ethanol. After the deproteinization with trichloroacetic acid, the polysaccharide RTPS-I was separated and purified by using DE-AE-Cellulose, DEAE-Sepharose FF and Sephadex G-200 column chromatography. The analysis of properties and structure was per-formed by using GC, HPGPC, IR and NMR. Results:RTPS-I was a white flocculent solid after vacuum freeze-drying, and soluble in water. It contained three elements (carbon, hydrogen and oxygen) with the specific rotation [α]25D (H2O) of +164. 44 and the relative molecular mass of 17555. The glycosyl in RTPS- I was composed of glucose without uronic acid. The sugar ring was pyranoid ring, and each monosaccharide was linked by α-glycosidic bond. Conclusion: A homogeneous immunoactive polysaccharide RTPS- I from Trichosanthis Radix is isolated for the first time.