Ex situ nitrification followed by denitrification inside the landfill has been recommended to removeammonia from leachate. The effects of increasing nitrate load and decreasing organic carbon content inthe injected leachate on the denitrifying capacity of municipal solid waste (MSW) were investigated.Results showed that MSWpossesses a high denitrification capacity. Nitrate reduction could be initiatedwithin 48 h after the first addition of nitrate. Nitrate reduction rate increased with the increasing nitrateloading concentration. When the nitrate loading concentration was increased to 850 mg L_1, nitratereduction rate reached up to 35 mg L_1 h_1. Nitrite accumulation could be found after the addition ofnitrate in each test. However, the maximum nitrite accumulation efficiency declined with increasednitrate load. Organic carbon played an important role in the reduction of nitrate, and both endogenousand exogenous organic materials could act as electron donors.