Abstract: Stichopus japonicus Selenka, a kind of sea cucumber, has long been used in traditional Chinese medicine. An antitumor polysaccharide was extracted by hydrolysing its cell wall with both pepsin and pancreas homogenate followed by fractional precipitation with alcohol. After decolorization, the crude product was further purified by chromatography on a DEAE-cellulose column. The polysaccharide was obtained in acetate buffers (pH 6.0)containing 0.8 M NaGl0 as eluate. By electrophoretic and ultracentrifugal analysis, the preparation was shown to be quite pure. The specific rotation, intrinsic viscosity and sedimentation constant were measured, and a high metachromatic activity was demonstrated. The component sugars of the polysaccharide were identified as. galactosamine, hexuronic acid, fucose and sulfate, and their molar ratio was about 1:1: 1: 4, respectively. Thus the sulfated mucopolysaccharide obtained is widely different from all the known acidic polysaccharides isolated previously from sea cucumbers including stichopus iaponicus.