Ammonia-oxidizing archaea (AOA) play an important role in the oxidation of ammonia. However, the participation of AOA in the composting process has not been established. The addition of AOA to a compost mix was able to speed up both the onset of the hyperthermic phase and the composting time. The composition of the microflora and the relative abundance were determined by using denaturing gradient gel electrophoresis and quantitative real-time PCR, based on the presence of the archaeal amoA genes. The amplicon profiles allowed some of the major AOA species present in the final compost to be identified, and their relative abundance to be estimated from their amplification intensity. The lower pH during the lower temperature phase of compost served to enhance the nitrogen content of the final compost. The addition of AOA resulted in the expanding diversity of microflora species than that of the natural colonization. Crown Copyright (c) 2012 Published by Elsevier Ltd. All rights reserved.