This study was performed to evaluate the effect of aeration/mixing time(A/M), for the removal of organics, nitrogen and phosphorus in sewage by SBR, which is one of the biological treatment processes. The A/M was controlled each 1.5/4.5, 3.0/3.0, 4.5/1.5, 6.0/0.0(hr/hr). Here, the fill time was 6 hours and the aeration/mixing repeat cycle was 3 times. The results of this study were as follows; (1) The organics removal efficiency was increased in proportion to the A/M. (2) The SVI was supported under 120 and the sludge bulking didn`t occur on all operation conditions. (3) Although the NH₄^+-N removal efficiency was increased as the A/M was higher, the T-N removal efficiency was increased as that was lower. (4) As A/M was lower, the T-P removal efficiency was increased.