The gut microbiota significantly influences intestinal immunity through tryptophan (Trp) metabolism. Trp and its metabolites, including kynurenines, serotonin, melatonin, and bacterial-derived compounds like indole, play crucial roles in maintaining gut immune homeostasis and modulating the host-microbiota interaction. The aryl hydrocarbon receptor (AhR), a key regulator of immune responses, is activated by Trp metabolites, which help maintain immune balance. The gut microbiota can modulate Trp metabolism, affecting the availability of Trp and its metabolites, which in turn influence immune responses and intestinal health. Factors such as aging, stress, probiotics, and diseases like inflammatory bowel disease can alter Trp metabolism and its interaction with the microbiota. Understanding these interactions is essential for developing microbiota-based diagnostics and interventions to prevent or treat intestinal inflammation. The review highlights the complex interplay between the gut microbiota, Trp metabolism, and the immune system, emphasizing the importance of studying Trp metabolites for better understanding of gut immunity. The review also discusses the role of various Trp metabolites in immune regulation, including their effects on inflammatory responses, antimicrobial peptides, and immune cell function. The findings suggest that manipulating Trp metabolism through diet or probiotics could be a promising approach to modulate intestinal immunity and improve gut health.The gut microbiota significantly influences intestinal immunity through tryptophan (Trp) metabolism. Trp and its metabolites, including kynurenines, serotonin, melatonin, and bacterial-derived compounds like indole, play crucial roles in maintaining gut immune homeostasis and modulating the host-microbiota interaction. The aryl hydrocarbon receptor (AhR), a key regulator of immune responses, is activated by Trp metabolites, which help maintain immune balance. The gut microbiota can modulate Trp metabolism, affecting the availability of Trp and its metabolites, which in turn influence immune responses and intestinal health. Factors such as aging, stress, probiotics, and diseases like inflammatory bowel disease can alter Trp metabolism and its interaction with the microbiota. Understanding these interactions is essential for developing microbiota-based diagnostics and interventions to prevent or treat intestinal inflammation. The review highlights the complex interplay between the gut microbiota, Trp metabolism, and the immune system, emphasizing the importance of studying Trp metabolites for better understanding of gut immunity. The review also discusses the role of various Trp metabolites in immune regulation, including their effects on inflammatory responses, antimicrobial peptides, and immune cell function. The findings suggest that manipulating Trp metabolism through diet or probiotics could be a promising approach to modulate intestinal immunity and improve gut health.