Abstract: In order to study the physicochemical properties,structure and immunological activity of Huangshan floral mushroom polysaccharide FMP3-1,a homogeneous polysaccharide FMP3-1 was obtained from Huangshan floral mushroom by hot water extraction and purified by DEAE-Cellulose and Sephacryl S-300 dextran gel. Furthermore,the chemical structure of FMP3-1 was analyzed by means of HPGPC,GC,GC-MS,NMR and partial acid hydrolysis. Meanwhile,the immunological activity of FMP3-1 and its acid hydrolysate component FMP3-1S were studied. The results showed that the molecular weight of FMP3-1 was 5.74×10⁵ Da. FMP3-1 was mainly composed of mannose,glucose and galactose with a molar ratio of 1.00:9.23:0.57. The backbone of FMP3-1 was consisted of(1→4)-β-D-Glcp,(1→6)-β-D-Glcp and(1→6)-β-D-Manp with 1-β-D-Glcp and 1-β-D-Galp as the branched chains substituted at O-3 position of(1→6)-β-D-Glcp and(1→6)-β-D-Manp. Immunological activity study showed that FMP3-1 could promote the proliferation,NO production and phagocytosis of Raw 264.7 macrophages,displaying a good immunological activity,which was greatly affected by its branched chain.