This study was conducted to verify and discuss the denitrifying dephosphatation under different levels of nitrate concentration and retention time of anoxic/aerobic process in a Sequencing Batch Reactor(SBR).The results of tests demonstrated that there were two kinds of phosph01MS-accumulating organisms(PAOs)in the biological excess phosphorus removal(BEPR)system．One was non-DNPAOs that could only use oxygen as terminal electron acceptors, the other was denitrifying PAOs(DNPAOs)that could use both nitrate and oxygen as terminal electron acceptors. Phosphorus uptake efficiency could be attained under anoxic period ranging from 28.7%-96.7% in an anaerobic/anoxic/aerobic system Experimental results showed that nitrate concentra-tion and retention time of anoxic/aerobic process were the key factors affecting the course of denitrifying dephos-phatation.