Phosphorus contents and phosphorus-releasing bacteria were characterized in a small eutrophic lake, Eastern China. Total phosphorus and water soluble inorganic phosphate (WSIP) in water bodies were as high as the levels of hyper-eutrophic lakes. Calcium bound phosphate and organic phosphorus were 2 major forms of phosphorus existing in the sediments. Enumeration of inorganic phosphate-solubilizing bacteria (IPB) and organic phosphorus-mineralizing bacteria (OPB) with culture-dependent method showed that these bacterial groups were not very rich in the ecosystem. Molecular identification and phylogenetic analysis of the predominant IPB and OPB strains indicated that there existed various kinds of bacteria participating in the phosphorus release. Laboratory tests on phosphorus release abilities showed IPB strains could liberate more than 50 microgml(-1), while OPB strains produced less than 2 microgml(-1) WSIP every day.