The collective of microflora inhabiting human mouth is called oral microbiota. Increasing evidence has proven that oral microbiota is highly associated with not only oral but also systematic diseases. Comprehensive knowledge of oral microbiota has been obtained after the launch of Human Microbiome Project, as well as some other microbial metagenomic projects. This paper reviewed the latest research on composition, succession, and potential impacts of oral microbiota on systemic diseases and health.