Abstract： Objective To compare the intraradicular bacterial community structures of teeth with or without post-treatment periapical periodontitis and to explore the suspicious microorganisms that is related to persistent periapical infection.Methods The intraradicular biofilm samples were collected from 10 post-treatment periapical periodontitis teeth(apical periodontitis group) and 10 teeth without post-treatment periapical periodontitis(without apical periodontitis group).The V 1-V3 hypervariable regions of bacterial 16S rRNA genes were amplified,and the high-throughput pyrosequencing was performed.The composition and structure characteristic of intraradicular microbiome were revealed by bioinformatic analysis.Results Total sequences were taxonomically classified into 132 species-level bacteria belonging to 96 genera and 21 phyla.The most representive phyla in apical periodontitis group were Firmicutes[32％ (18 534/58 688)],Proteobacteria[27％(15 626/58 688)],Actinobacteria[15％ (8 685/58 688)],Bacteroidetes [11％ (6163/58 688)],Fusobacteria[8％ (4761/58688)] and Spirochaetes[3％(1 785/58 688)].While the most representive phyla in without apical periodontitis group were Firmicutes[31％(16 941/55 480)],Proteobacteria [27％(14 748/55 480)],Bacteroidetes [18％(9 948/55 480)],Fusobacteria[10％(5 307/55 480)],Actinobacteria [9％(4 761/55 480)],Chloroflexi[3％(1 785/55 480)].The abundance of actinobacteria in apical periodontitis group was significantly higher than without apical periodontitis group(P＜0.01).The detection rates of actinomycetes in apical periodontitis group and without apical periodontitis group were 100％ and 50％.Conclusions The diversity of intraradicular bacterial community in teeth with apical periodontitis was higher than those without apical periodontitis.Actinomycetes may be related to post-treatment periapical periodontitis.