Bacteria　are　ubiquitous　and　abundant　in　the　atmosphere　and　some　of　them　are　potential　pathogens　known　to　cause　diseases　or　allergies　in　humans.　However,　the　quantities　and　compositions　of　total　airborne　bacterial　community　and　their　relationships　with　environmental　factors　remain　poorly　investigated.　Here,　a　case　study　of　the　total　airborne　bacteria　of　PM2.5　collected　at　six　cities　in　Beijing-Tianjin-Hebei　(BTH)　megalopolis,　China　were　profiled　using　quantitative　polymerase　chain　reaction　(qPCR)　and　Illumina　MiSeq　(PE300)　sequencing.　qPCR　results　showed　the　high　abundance　of　total　airborne　bacteria　of　PM2.5　in　BTH,　ranging　from　4.82　x　10(4)　+/-　1.58　x　10(3)　to　2.64　x　10(5)　+/-　9.63　x　10(4)　cell　m(-3)　air,　and　averaged　1.19　x　10(5)　cell　m(-3)　air.　The　six　PM2.(5)　samples　were　classified　into　three　groups.　Proteobacteria,　Cyanobacteria,　Actinobacteria　and　Firmicutes　were　the　four　dominant　phyla　of　PM2.5.　18　common　potential　pathogens　with　extremely　low　percentage　(3.61%)　were　observed,　which　were　dominated　by　Enterococcus　faecium　and　Escherichia　coli.　Plants　and　soil　are　probably　the　main　sources　of　bacteria　in　PM2.5,　as　suggested　by　the　high　percentages　of　Chloroplast,　plant-associated　bacteria　(e.g.,　Rhizobiales　and　Sphingomonadales)　and　soil-inhabiting　bacteria　(e.g.,　Burkholderiales　and　Pseudomonadales).　Variation　partitioning　analysis　(VPA)　indicated　that　the　atmospheric　pollutants　explained　the　most　of　the　variation　(31.90%)　in　community　structure　of　PM2.5,　followed　by　meteorological　conditions　(15.73%)　and　the　chemical　compositions　of　PM2.5　(11.32%).　The　case　study　furthers　our　understanding　of　the　diversity　and　composition　of　airborne　bacterial　communities　of　PM2.5　in　BTH,　and　also　identified　the　main　factors　shaping　the　bacterial　communities.