ABSTRACT: An extracellular polysaccharide from Ensifer sp, named GS501, was purified by a series of steps including ethanol precipitation, protein removal, ion exchange chromatography and gel filter chromatography. Then the characteristics of GS501 were analyzed. The monosaccharide composition analysis was performed by high performance liquid chromatography. The result showed that GS501 was mainly composed of glucose, which was in accord with infrared spectroscopy analysis. Scanning electron microscope analysis showed that GS501 had a gully and loose surface structure, which may be in favor of adsorption and flocculation.