Objective　To　study　the　structure　and　immunomodulatory　activity　of　homogeneous　polysaccharides　isolated　from　Fangfeng　(Saposhnikoviae　Radix).　Methods　Polysaccharide　SP800203　was　isolated　from　Saposhnikoviae　Radix　by　several　chromatographic　techniques,　such　as　DEAE-Cellulose　and　Sephadex　G-75.　The　relative　molecular　weight,　monosaccharide　composition,　oligosaccharide　fragments,　sugar　residue　types　and　glucosidic　bond　linkage　modes　were　characterized　with　ESI-MSn,　GC-MS,　and　NMR.　Cell　and　zebrafish　experiments　were　used　to　explore　the　immunomodulatory　activity　of　polysaccharide　SP800203.　Results　Polysaccharide　SP800203　was　isolated　from　Saposhnikoviae　Radix,　with　a　glucuronic　acid　content　of　75.73%,　a　molecular　weight　of　7.14×104,　composed　of　rhamnose　(Rha),　galactose　(Gal),　arabinose　(Ara),　and　galacturonic　acid　(GalA),　the　molar　ratio　of　monosaccharides　was　2.8:6.7:6:84.5.　The　main　chain　was　polymerized　by　GalA,　and　the　two　branch　chains　were　separately　polymerized　by　Ara,　GalA,　Gal,　Rha　and　Ara,　GalA,　Gal,　which　were　connected　to　the　backbone　by　β　and　α　glycosidic　bonds,　respectively.　Polysaccharide　SP800203　could　significantly　promote　the　release　of　NO,　TNF-α,　IL-1β,　IL-6　and　increase　the　density　of　immune　cells　and　the　number　of　macrophages.　Conclusion　Polysaccharide　SP800203　is　a　new　homogeneous　polysaccharide　isolated　from　Saposhnikoviae　Radix,　which　shows　good　immunomodulatory　activity.　The　results　of　the　study　lay　a　foundation　for　elucidating　the　mechanism　of　immune　regulation　of　Saposhnikoviae　Radix,　and　provide　a　scientific　basis　for　the　clinical　application　and　further　research　of　Saposhnikoviae　Radix.　©　2024　Editorial　Office　of　Chinese　Traditional　and　Herbal　Drugs.　All　rights　reserved.