Abstract: The water-soluble polysaccharide is isolated and purified from the seeds of Sesbania cannabina (Retz.) Pers. Its physiochemical properties are investigated. The purified preparation seems to be homogeneous after ultra-centrifugation. The sedimentation coefficient of the gum obtained from alcoholic purification is 4.71 S, its intrinsic viscosity is 5.93 dl/g and its molecular weight is estimated to be 391,000. When it is obtained from copper alcoholic purification, however, its sedimentation coefficient is 2.82 S, its intrinsic viscosity 2.44 dl/g and its molecular weight 206,000. Several derivatives of the gum have been prepared, including carboxymethylated gum, hydroxyethylated gum and carboxymethylhydroxyethylated gum.