From the pods of Opuntia dillenii a polysaccharide was isolated in 0.5 % yield (based on the weight of the fresh material). The poly sacch aride is composed of arabinose and galactose in the molar ratio 1 :3. On the basis of the results of oxidation and characterization and estimation of the methylated sugars in the methylated poly sacch aride, a probable structure has been suggested for the arabinogalactan.