Enhanced biological phosphorus removal (EBPR) was operated in a laboratory-scale sequencing batch reactor (SBR). Fluorenscent in situ hybridization (FISH) was used to study the competition between the phosphate-accumulating organisms (PAOs) and glycogen-accumulating organisms (GAOs). The influence of competition between PAOs and GAOs on phosphate removal efficiency was discussed. The results showed that 0-20 d was an adjusting stage. COD and phosphate removal efficiencies of SBR were unstable. PAOs and GAOs competed for the predominant status in reactor. During 20-60 d,the amount of PAOs increased gradually,while the amount of Alphaproteobacteria decreased and Gammaproteobacteria contents was below 8. 11% in this stage,which indicates that low temperature is beneficial to PAOs. PAOs proliferated rapidly during 50-60 d. Because the increased amount of PAOs was only 3. 2% per 5 d,the phosphate removal efficiency in reactor was not delayed.