Cassia hirsuta Linn. seeds yielded a water soluble polysaccharide as D-galactose and Dmannose in 1:4 molar ratio by alkaline hypoiodite method on paper chromatogram. Reactions of the periodate oxidation is one of the most important in the structure determination of seeds polysaccharide in carbohydrate chemistry. Periodate oxidation method was done with sodium metaperiodate as oxidant and it was proposed by Malaprade and Flurry & Lange‘s method. The mole of periodate consumption and formic acid liberation during periodate oxidation reaction of seeds polysaccharide was determined volumetrically. Composition and probable polysaccharide structures have also been elucidated with the information obtained from periodate oxidation of seeds polysaccharide. After complete periodate oxidation reaction, it consumed 1.13 moles of oxidant with simultaneous liberation of 0.23 moles of formic acid per mole of anhydrohexose sugar unit of the polymer chain after 30 hrs. Formic acid appear is to be originating from the reducing as well as non - reducing terminal unit of D-galactose and D-mannose are of (1®6)-a- type at non-reducing end while (1®4)-b-type at main polymer chain between D-mannose residues.