Abstract: Ramaria botrytoides RBP-Ⅰ was isolated and purified from Ramaria botrytoides through water extraction identified as homogeneous polysaccharide by gel permeation chromatography and Sephadex G-100 arbitration.The contents of total sugar, starch, protein and union acid were analyzed by phenol-sulfuric acid, law of iodine-potassium iodide, coomassie brilliant blue stain and sulfuric-carbazole method. The structure and monosaccharide composition were studied by infrared ( IR) spectra analysis and gas chromatograph.The results showed that the average molecular of RBP-Ⅰ was 15857 Da, the total sugar was86.94%, the uronic acid was 5.14% with no starch and protein.It was composed of rhamnose, fucose, arabinose, manose, glucose and galactose with a mole ratio of 1.00∶ 6.53∶ 1.99∶ 8.29∶ 70.05 ∶ 53.80.RBP-Ⅰexhibited characteristic absorption peak of polysaccharide by IR, indicating that it was pyranoid polysaccharide.Moreover, at 10000 μg/m L of RBP-Ⅰ, the FRAP value was 0.0672 mmol/L, the scavenging rate was 22.83% and 15.71% for DPPH and ABTS+· respectively. These results suggested that RBP-Ⅰhad potent antioxidant activity.