Abstract: An upflow microaerobic-oxic (M/O) process was proposed. During this process an upflow column was controlled under low dissolved oxygen by aeration to replace the rectangular anoxic reactor controlled by mixer. A comparative study on wastewater treatment performance was conducted using the two systems under the same operation condition. The results showed that under the condition that hydraulic retention time (HRT) lasted 12h and the sludge recycle ratio was 200% (inner) and 50% (outer), the average COD_Cr removal efficiency of M/O and A/O were 88.0% and 83.0%, respectively. COD_Cr removal efficiencies of M/O process achieved 6% higher than that of A/O and the effluent. The COD_Cr contents of both systems were below 50mg/L. The difference of ammonia removal efficiencies between M/O and A/O was not obvious and achieved at 95.0% and 93.3%, respectively. However, there was a significant difference of total nitrogen (TN) removal effect and the average removal efficiency of M/O was 16% higher than that of A/O, and the TN removal efficiency for M/O was 67.5%. During nearly 160day''s operation, M/O process appeared more stable, lower fluctuation of effluent water quality, higher resistance to shock loading than A/O, especially strengthened the TN removal.