Abstract: In order to investigate the variations of specific oxygen uptake rate(R_SOUR) and its feasibility during nitrification as a control parameter in activated sludge system,a method was presented realizing on-line determination and feedback in SBR process.Two SBRs were seeded with activated sludge of nitrite-oxidizing bacteria (NOB) and nitrite-oxidizing bacteria(AOB) as the dominant bacteria,respectively.The variations of SOUR under constant dissolved oxygen concentration were studied and results showed R_SOUR of SBR1 decreased dramatically from 0.01 to 0.004mg O₂ per gram and minute,after 290min aerobic reaction time,while that of SBR2 declined from 0.074 to 0.013mg O₂ per gram and minute,after 206min aerobic reaction time at the completion of ammonium oxidation.The sharp decline of R_SOUR indicated the completion of nitrification,then aeration should be terminated.R_SOUR curve can exactly reflect the process of nitrification,all of which may well lay a theoretical foundation for application of SOUR as on-line control parameters.