A well-balanced oral microbiome, in harmony with the host, is critical for promoting and maintaining oral and general health. Growing evidence has suggested that the oral microbiota is closely linked to human systemic diseases, including diabetes, obesity, and a wide range of cancers. The associations between oral microbiota and tumor are classified into two categories. First, certain microorganisms are definitely involved in tumorigenesis. Secondly, oral microbiota is not directly involved in the development of tumors, but consistent changes in the composition of oral microbiota have been observed in patients of the same tumor, making it a potential tool for tumor diagnosis. However, how it alters oral microbiota remains unclear. The relationship between oral microbiota and distant tumors still requires further elucidation. Our previous studies have revealed significant alterations of salivary glycopatterns, which played an important role in natural regulation of the oral microbiota dysbiosis in gastric cancer patients. These results provided a new insight into the relationship between oral microbiota and distal tumors, which need deeper, broader, and more rigorous research.