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To study the long-term effect of dissolved oxygen (DO) on phosphorus removal process, the characteristics of enhanced biological phosphorus removal (EBPR) under the DO level of 5.5 -7.0 mg/L and 0.5 - 1.5 mg/L were investigated systematically using sequencing batch reactor (SBR). The results showed that, when pH was in 7.2 - 7.6 and temperature was at (23 ± 0.5 ) °C , high DO had adverse impact on both phosphorus release process and phosphorus uptake process. The amount of released phosphorus in anaerobic period was 43.08% lower than that under low DO condition. Phosphorus uptake process went fast during the initial 30 rain in aerobic period. The maximum specific phosphorus uptake rate was 6.27, 11.45 mg ⋅ g-1 ⋅ h-1 under high DO and low DO conditions, respectively. Analysis indicated that the main reason of deterioration of phosphorus removal process was deficiency of poly - β - hydroxybutyrate (PHB) caused by excessive aeration and more influent carbon source used for densification process. High DO did not have obvious advantage on restraining filamentous sludge bulking than low DO. The improvement of phosphorus removal was usually associated with the improvement of sludge settleability. [ABSTRACT FROM AUTHOR]