In order to improve reactor performance of existing sewage treatment plant, feasibility of enhancing reactor performance by bioaugmentation using EM as bioaugmentation agent and effects of anoxic : oxic time ratio on reactor performance were investigated. Continuous and intermittent aeration mode were compared under the 6hr of HRT. Three different type of intermittent aeration modes, that is, 15 min. of anoxic : 45 min. of oxic, 30 min. of anoxic : 30 min. of oxic and 45 min. of anoxic : 15 min. of oxic, respectively were chosen as test modes to study the effect of anoxic: oxic time ratios on reactor performance. Optimum anoxic : oxic time ratio was 30 min. : 30 min. when considering simultaneous removal of organic, nitrogen and phosphorus. When applying EM into continuously aerated reactor under the varying dosing rates of 50~200 ppm, reactor performance in terms of organic and nitrogen removal efficiencies was not improved at all. Nitrogen removal efficiency was increased when the EM dosing rate was increased. However, the degree of improvement was slight when the EM was injected above 100 ppm. However, optimum phosphorus removal was found at the EM dosing rate of 200 ppm. Thus, it was found that optimum injection concentration of EM is 200 ppm. It is apparent that putting EM into sewage treatment plant affect T-N removal efficiency significantly. Based on results obtained from this study, EM application render improving T-N removal efficiency of reactor by enhancing denitrification efficiency especially in operation conditions of relatively long anoxic period. To make reciprocal condition in reactor with intermittent aeration is prerequisite in enhancing reactor performance through EM injection. In case of modifying existing continuously aerated reactor into intermittently aerated reactor, it is obvious that operating cost of aeration would be reduced by reducing aeration time compared with existing conventional sewage treatment plant.