This study was conducted to investigate the ratios of phosphorus release to COD uptake, phosphorus release to nitrate removal, and phosphorus uptake to phosphorus release by denitrifying phosphate accumulating organisms in the system composed of an anaerobic reactor and an anoxic reactor as the change of the influent nitrate loading. The influent concentrations of COD, NH₄?-N and PO₄-P were 300, 20 and 6 ㎎/L, respectively, whereas the influent nitrate concentrations were varied at 10, 15,20 and 30 ㎎/L, As a result, the ratio of phosphorus release to carbon uptake was increased in accordance with nitrate supply. The denitrifying phosphate accumulating organisms simultaneously took up phosphate and removed nitrate from the anoxic reactor. With above 20 ㎎/L of sufficient NO₃?-N supply, phosphate was taken up excessively by the DNPAOs in anoxic condition, resulting in the ratio of phosphorus uptake to nitrate removal to be 1.97. The large amount of both uptake and release of phosphorus occurred above 20 ㎎/ L of nitrate supply, achieving the ratio of phosphorus uptake to phosphorus release to be 1.05. Conversely, if nitrate as the electron acceptor was limited, the ratio was found to be low.