This study evaluated the on-site treatment of a weak municipal landfill leachate with a Rotating Biological Contactor (RBC) at pilot scale (0.9 m dia.). The leachate generally had COD and NH3-N values of less than 1000 mg/L and 50 mg/L respectively. A high treatment efficiency for both carbon removal and nitrification was achieved despite variable and intermittent loading conditions. The effluent filtrable BOD5 was generally less than 10 mg/L and the effluent NH3-N concentration was usually less than 1.0 mg/L. This effluent quality was achieved at mass loading levels comparable to those for sewage treatment (10.0 kg BOD5/ 1000 m2 · d for carbon removal and 0.7 kg TKN/1000 m2·d). An aside to this study showed that trace organics, some of which are on the EPA priority pollutant list, were present in this leachate and were effectively removed by the RBC.