Abstract: Based on inhibitor acetylene (C₂H₂), ammonium addition and batch incubation, the contribution of ammonium-oxidizing bacteria to the process of landfill methane (CH₄) oxidation and the inhibition effect by ammonium addition have been analyzed. Four different types of materials have been sampled:landfill covered soil, mineralized refuse, sandy soil and clay soil under the condition of the initial CH_{4concentration} of 16% to simulate landfills environment. The contributions of ammonia-oxidizing bacteria to CH_4oxidation ranged from 5.64% to 16.24% and following the followed increasing order:sandy soil4oxidation were confirmed from 11.90% to 24.84% in the four tested samples, which followed the order as sandy soil4oxidation in landfill samples were significantly higher than those for sandy soil and clay soil.