Simultaneous removal of total organic carbon (TOC) and nitrogen (T-N) by a plunging liquid jet bioreactor was investigated for small-scale treatment of domestic wastewater The bioreactor was operated under suspended growth and attached growth conditions and intermittent aeration to carry out both nutrification and denitrification processes in one vessel. In the suspended growth system, TOC removal efficiency was about 90% but nitrogen removal was about 50%. The nitrogen removal was nor sufficient because nitrification was a rate-limiting step. To overcome this limitation a biomass carrier was inserted in the reactor In the attached growth system, nitrification proceeded almost completely and, hence, nitrogen removal was increased. TOC and nitrogen removal efficiency was 97% (effluent TOC concentration was about 3.0 mg/l) and 84% (effluent T-N concentration was about 2.0 mg/l) in the oxic periods, respectively, and those were 93% (TOC concentration was about 5.5 mg/l) and 90% (T-N concentration was about 1.2 mg/l) in the anoxic periods This effluent T-N concentration satisfies the severest target value for T-N discharge concentration in small-scale domestic wastewater treatment in Japan. The bioreactor system with the biomass carrier operated under intermittent aeration was judged to be excellent for simultaneous removal of TOC and nitrogen in small-scale treatment of domestic wastewater.