Purpose: Gut microbiota is predicted to play a key role in manifestation of gastrointestinal tract cancers. The human gastrointestinal tract is a complex and abundant network of microbial community. Gut microbiota depicts the microbe population living in our intestine. Humans harbour more than 1014 microbes in the gut, and the diversity and densities of the microbiota increase from stomach to colon. Methods: The beneficial relationship between endogenous microbiota and the eukaryotic hosts helps in maintaining various metabolic activities of the body as well as temperature and pH balance. Studies using culturing methods have suggested that the oesophagus is either sterile or contains only a few transient microbes that originates from the oropharynx by swallowing or from the stomach by gastroesophageal reflux. However, metagenomics suggest that large numbers of uncultured organisms are harboured in the human gut. Results: Observations suggest that research directed towards manipulation of the gut microbiota can be employed in prevention as well as treatment of these conditions. Well-designed, randomized, placebo-controlled human studies using probiotics and/or prebiotics are necessary to formulate the directions for prevention and therapy. Conclusions: Change in gut microbes in gastrointestinal (GI) tract may have major implication in gastric cancer, the fifth most occurring malignancy in the world. Affected population manifests multiple conditions and diseases, which majorly includes inflammatory bowel disease and colorectal malignancy. © 2016, Springer Science+Business Media New York.