This study was carried out to investigate the effects of influent NH₄⁺-N load, C/N ratio, and superficial air velocity on the biological nitrogen removal efficiencies of a biological aerated filter. The laboratory scale upflow anoxic-oxic biological aerated filter(AO-BAF) with porous ceramic media was continuously operated for nitrification and denitrification with synthetic wastewater. Various influent C/N ratios and superficial air velocity had been applied to investigate their effects on nitrogen removal. The AO-BAF showed more than 90% NH₄⁺-N removal efficiencies in the ranges of 0.26-1.76 kg NH₄⁺-N/m³·d and an average 65% of T-N removal efficiencies at the C/N ratio of 1. The reactor is very compact in size when considering the empty bed contact time(EBCT) of 1. 1 h and the hydraulic retention time(void fraction: 35%) of 0.38 h. The average T-N removal efficiencies were increased with the superficial air velocity because of the enhanced nitrification efficiencies. Some parts of the denitrification occurred in aerobic nitrification zone where organic carbons are rarely available. It is likely that the denitrification without organic carbon may be the anaerobic ammonium oxidation due to the oxygen mass transfer resistance within the biofilms even though the mechanism is still unclear.