The gut microbiota plays a critical role in maintaining intestinal immune homeostasis and influencing the host's immune response through tryptophan (Trp) metabolism. Trp, along with its metabolites such as kynurenines, serotonin, and melatonin, and bacterial-derived metabolites like indole and skatole, significantly impact gut microbial composition, immune function, and host-microbiome interactions. The aryl hydrocarbon receptor (AhR), a key mediator of Trp metabolite effects, regulates immune homeostasis and intestinal immunity. Trp metabolism is influenced by factors such as aging, stress, probiotics, and diseases, which can modulate the gut microbiota-immune system interaction. This review highlights the complex interplay between the gut microbiota and Trp metabolism, emphasizing the role of AhR in regulating immune responses. Understanding these interactions provides insights into potential therapeutic strategies for intestinal disorders. The review also discusses the influence of endogenous and bacterial Trp metabolites on immune homeostasis, highlighting the importance of targeted analysis of these metabolites for accurate experimental results. The review underscores the need for further research to clarify the mechanisms by which the gut microbiota modulates intestinal immunity through Trp metabolism, which could lead to innovative microbiota-based diagnostics and nutritional interventions for preventing or alleviating intestinal inflammation.The gut microbiota plays a critical role in maintaining intestinal immune homeostasis and influencing the host's immune response through tryptophan (Trp) metabolism. Trp, along with its metabolites such as kynurenines, serotonin, and melatonin, and bacterial-derived metabolites like indole and skatole, significantly impact gut microbial composition, immune function, and host-microbiome interactions. The aryl hydrocarbon receptor (AhR), a key mediator of Trp metabolite effects, regulates immune homeostasis and intestinal immunity. Trp metabolism is influenced by factors such as aging, stress, probiotics, and diseases, which can modulate the gut microbiota-immune system interaction. This review highlights the complex interplay between the gut microbiota and Trp metabolism, emphasizing the role of AhR in regulating immune responses. Understanding these interactions provides insights into potential therapeutic strategies for intestinal disorders. The review also discusses the influence of endogenous and bacterial Trp metabolites on immune homeostasis, highlighting the importance of targeted analysis of these metabolites for accurate experimental results. The review underscores the need for further research to clarify the mechanisms by which the gut microbiota modulates intestinal immunity through Trp metabolism, which could lead to innovative microbiota-based diagnostics and nutritional interventions for preventing or alleviating intestinal inflammation.