Water-soluble polysaccharides were isolated from Tetragonia tetragonoides (Aizoaceae), and their anti-inflammatory effects on carrageenan-induced edema and adjuvant arthritis were tested. One of the active fractions TII_c, gave a single peak on high-performance liquid chromatography and gel filtration. Methylation, periodate oxidation and carbon-13 nuclear magnetic reasonance spectroscopic studies suggested that TII_c is composed of the following repeating unit : [numerical formula]