Abstract: For the landfill leachate treatment, it is hard to achieve nitrogen removal effectively without external addition of organic carbon source. To solve this engineering problem, a pilot-scale AO-MBR process was developed in this study to remove the high loading organics and nitrogen by nitritation-denitritation in raw municipal landfill leachate. The stability and performance of the pilot-scale AO-MBR process under different influent ρ(C)/ρ(N) mass ratios were investigated. The results of this study showed that the removal efficiencies of COD and TN were above 80% with influent ammonia concentration of 1 500 mg/L, ρ(C)/ρ(N) mass ratio of above 2, and hydraulic retention time (HRT) of 4.21 d. It indicates that the pilot-scale AO-MBR process successfully achieves efficient biological removal of ammonia from raw landfill leachate with low ρ(C)/ρ(N) mass ratio.