To explore the correlations of tongue coating changes with and tongue coating microbiota and gut microbiota in the patients with greasy tongue coating and colorectal cancer.Methods:A total of 63 patients with colorectal cancer treated in the Department of Colorectal Surgery of the First Affiliated Hospital of Harbin Medical University from September 2022 to March 2023 were enrolled in this study.Based on the characteristics of tongue coatings，12 patients with yellow greasy tongue coating and 9 patients with white greasy tongue coating were selected by stratified random sampling，and the tongue coating，cancer tissue，and adjacent tissue were sampled from these patients.Meanwhile，tongue coating samples were collected from 6 healthy volunteers with thin white tongue coating and no abnormalities during colonoscopy as the control group.All the samples were subjected to high-throughput 5R 16S rDNA sequencing.Results:The patients with colorectal cancer mainly presented yellow greasy tongue coating and white greasy tongue coating.Atopobium in the tongue coating and Granulicatella in the gut might be characteristic bacteria in the patients with yellow greasy tongue coating.Gemella in the tongue coating and Roseburia and Shewanella in the gut might be characteristic bacterial genera in the patients with white greasy tongue coating.Fusobacterium nucleatum，Actinomyces odontolyticus，and Peptostreptococcus stomatis might be potential oral and intestinal bacteria in the colorectal cancer patients with yellow greasy tongue coating and white greasy tongue coating，respectively.Conclusion:The changes of tongue coating in colorectal cancer patients are related to the changes of the structure and abundance of gut microbiota and tongue coating microbiota.The different overlapping species and degrees between tongue coating microbiota，cancer tissue microbiota，and adjacent tissue microbiota suggest that the changes in greasy tongue coating in traditional Chinese medicine can reflect the characteristic changes in the oral and intestinal microbiota in the patients with colorectal cancer.The findings provide a theoretical basis for the later research on the Chinese medicines for colorectal cancer by targeting microorganisms.