Cassia laevigata Linn. seeds yielded a water soluble polysaccharide on acid hydrolysis as D-galactose and D-mannose in 5 : 2 molar ratio by TLC, coloum and paper chromatographic analysis. Upon periodate oxidation of seed polysaccharide with sodium metaperiodate, (0.125 M).It consumed 2.55 moles of periodate with simultaneous liberation of 1.00 moles of formic acid per mole of anhydrohexose unit after 60 hrs. On the basis of methylation results, the proposed water soluble seeds polysaccharide structure has been confirmed by periodate oxidation method.