Abstract: Objective： To analyze the diversity of Methanogenic archaea in endodontic infections and establish the phylogenetic tree based on functional gene mcrA. Methods：Using PCR and a pair of specific primers，mcrA was selectively amplified from total genomic DNA extracted from the microbial community in the root canal of endodontic infections. Positive clones were selected by blue-white screening, and the mcrA sequences were determined by DNA sequencing. ‘Clustalx’and ‘Mega 4’ software bags were used to analyze mcrA sequences. Phylogenetic analysis was carried out and the phylogenetic tree of methanogenic archaea was established. Results：Four root canals of endodontic infections were analyzed. We found one case positive for Methanogenic archaea. A phylogenetic tree based on functional gene mcrA was established. The mcrA fragments in endodontic infections showed high sequence similarity with Methanobrevibacter oralis. Conclusions： The diversity of Methanogenic archaea in the one sample from endodontic infections in this study was confined to Methanobrevibacter oralis-like sequence types.