Abstract: In this study, the effects of aeration ratio on organic materials removal rate in sequencing batch reactors was considered. Eight hours cycles, including 6 h aeration period, were applied. Raw wastewater with COD equal 350 ± 20 mg L-1 was prepared by dried confectionary milk and tap water. SOTE equation in test condition was defined as y=1.24981ln(x) +13.86231. Aeration ratio was described as ratio of supplied dissolved oxygen to required oxygen amount. Taking into account nitrification and denitrification processes, five aeration ratios: 1.1, 3.14, 5.44, 6.97 and 8.83 are applied. Results showed aeration ratios, above stoichiometric required oxygen amount, do not have a significant effect on organic materials removal efficiency and just slope of curve of COD changes via time, changed moderately.