A fuzzy controller to optimize oxic phase of sub-cycle in pilot scale SBR (working volume, 20m(3)) located at public swine wastewater treatment plant was investigated. The operation mode of intermittent feeding of raw water and sub-cycle with repeating anoxic-aeration conditions were adapted to avoid the high-strength nitrogen inhibition. In sub-cycle, aeration time for ammonium oxidation was tried to control by fuzzy system using DO value and its differential values for input membership function. In previous study, a lag time of DO profile was proved to be useful for inference of nitrogen loading rates and abrupt raise of DO showed potential ability to detect ending point of ammonia oxidation, however, it also needs proper safety factor for high level DO in lag time or noisy system. Here, the fuzzy system could reduce the complexity of application. As results, the fuzzy system with the simultaneous application of DO value and its differential values was appropriate for the stable control of SBR.