The Formosan subterranean termite, Coptotermes formosanus, is an invasive pest species obligatorily dependent on its gut microbiota.  The bacterial community of the FST gut remains largely undiscovered despite its importance in termite nutrition, gut ecology and potential usefulness for termite control.  In this study, bacterial diversity in the guts of termite workers from China (native range) and the U.S. (introduced range) was determined using 16S rRNA gene sequencing. The results were compared among colonies and regions to investigate how bacteria diversity changes across regions and to identify obligatory symbionts and termite-specific bacteria lineages.   To date, three colonies each from Louisiana and China, respectively, yielded 133 (108 novel species) and 88 species (73 novel species) out of 753 and 445 individual 16S rRNA gene sequences analyzed.  Many of the species were within the phyla Firmicutes (China, US; 40, 29) and Bacteroidetes (12, 22).  Spirochaetes were diverse in the Louisiana colonies (62) but only 6 species were present in the China colonies.  A Bacteroidales species previously discovered in other termites was predominant in all termite colonies from the introduced ranges (61%) and China (15%). Pilibacter termitis, a lactic acid bacterium previously isolated from C. formosanus from Hawaii and Louisiana, was highly abundant in the China colonies (17%).  These results show some similarities in the bacterial gut community between native and introduced termite populations, even though great differences exist.  Most species in this study phylogenetically clustered with gut bacteria found in related termite species, indicating co-evolution of bacterial symbionts with their hosts.