Abstract: This paper mainly discussed a flocculant-producing bacteria isolated from soil and the flocculating substance secreted into the medium.Preliminary studies identified the bacteria CCTCC M201005 as Nocardia species.Its growth and metabolism were studied.More than 80% of the flocculating activity was detected in the culture broth.A new bioflocculant--REA-11 was purified by repeated ethanol precipitation,ion exchange and gel chromatography from the culture broth.Its molecular mass was estimated to be over 10 ⁵g·mol ^-1 by the gel filtration method.The results of investigation on the purified REA-11 and its acid hydrolysate by colcrimetric analysis,paper chromatography,HPLC and GC-MS suggested that REA-11 was a novel acidic polysaccharide mainly composed of galactocuronic acid with little acetic acid but no hexosamine detected.Protein was not a necessary part for the flocculating activity of REA-11,but mainly assisting in connecting the monosaccharides in the macromolecule or maintaining the dimensional conformation of the active biopolymer.