AbstractThe oral cavity is an important window for the microbial communication between environment and the human body. The oral microbiome plays an important role in human health. Here, we analyzed 447 datasets from human oral samples published by the Earth Microbiome Project (EMP). The microbes in these human oral samples were taxonomically assigned to at least 266 genera of 18 bacterial and archaeal phyla. Among them, 11 genera with the relative abundance more than 1% were identified as 5 different bacterial phyla. Compared with 815 samples from human gut, nose/pharynx and skin, the oral microbiome showed significantly lower diversity and possessed fewer unknown species than those of other body parts, and had distinct differences in species composition from other body parts. In addition, the oral microbiome showed significant differences in the populations of different countries, which may be determined by the living environment and lifestyle/dietary habits. Finally, the correlation analysis showed highly similarity between the oral microbiome and the microbiomes of Aerosol (non-saline) and Surface (non-saline), two types of environmental microbial habitats related closely to human. Together, these findings expand our understanding to the human oral microbiome.