AIM To study the structural property of the bioactive component from the fermentation broth of Streptomyces 139 which can inhibit IL 1R. METHODS Polysaccharide 139A is extracted and purified by means of macroreticular resin Diaion HP 20, cation exchange and DEAE Sephadex A 25 chromatography. The sugar compositions were analyzed with GC, the linkage positions of 139A were determined by methylation and GC MS. RESULTS The bioactive component which can inhibit IL 1R is a kind of polysaccharides. CONCLUSION The components of 139A repeat units are conjectured.