Phyllanthus niruri is a well-known medicinal herb that is widely used in Asia, Africa, and South America. The characterization of two purified polysaccharides from the whole plant has been investigated. Methylation analysis and (13)C NMR spectroscopy showed the chemical structure of two xylans. A hot 15% aqueous KOH fraction yielded a linear beta-(1-->4)-linked xylan, and 2% aqueous KOH afforded a complex acidic heteroxylan, with a (1-->4)-linked beta-Xylp main chain, substituted by rhamnose, arabinose, and 4-O-methylglucuronic acid side chains. These contained nonreducing end-units of arabinose, xylose, galactose, glucose, and nonmethylated glucuronic acid.