Abstract: Ammonium nitrogen (NH₄⁺ -N) removal was investigated by using a novel suspended carrier. Honeycomb-like biofilms were formed among the columns on the suspended carrier. The bioreactor was operated at 24-29℃ and pH values of 7.8-8.2. When the influent COD and NH₄⁺ -N concentrations were below 300 mg·L^-1 and 78 mg·L^-1 respectively, the effluent COD and NH₄⁺ -N concentrations after 3 h operation were less than 50 mg·L^-1 and 2 mg·L^-1, respectively. After 4 h operation, when the in-fluent COD concentration varied from 150 to 350 mg·L^-1 and the NH₄⁺ -N concentration from 80 to 130 mg·L^-1, the corresponding effluent concentrations were below 46 mg·L^-1 and 3.5 mg·L^-1 respectively. The ammonium-nitrogen biodegradation rate in the suspended carrier biofilm reactor is greater than that in the conventional activated sludge system. The honeycomb structure increases the porous ratio, decreases the wall thickness of biofilm and favors mass transfer and oxygen pervasion into the interior of biofilm, which provides better conditions for nitrobacteria growth and improves NH₄⁺ -N removal efficiency