Abstract: The possibility of using nitrate as electron acceptor in biological phosphorus removal was studied in this paper,and the difference between nitrate and oxygen as electron acceptor was compared. The results indicated that polyphosphate accumulating organisms (PAOs) could use nitrate as electron acceptor for biological phosphorus removal instead of oxygen,but it would be inhibited if COD presented.The rate of taking up phosphate in anoxic stage was related to the concentration of nitrate:the higher the concentration of nitrate was,the higher rate of taking up phosphate was obtained.The continuous and steady addition of nitrate is of benefit to phosphate removal.The efficiency of PHA digestion in the system using nitrate as electron acceptor is lower than using oxygen.The ratio of removed phosphorus to consumed PHA under anoxic condition was 0 63,which was 24% lower than 0.83 under aerobic condition;the amount of phosphorus taken up to per mole of electrons transferred under anoxic condition was 0 14 mol,which was 39 1% lower than 0 23 mol with oxygen as the electron acceptor.