The gut microbiome plays a critical role in cancer immunotherapy, influencing treatment efficacy and patient outcomes. Immunotherapy, particularly immune checkpoint inhibitors (ICIs), has shown promise in cancer treatment, but its effectiveness varies among patients. The gut microbiome, including bacteria, viruses, and fungi, interacts with the immune system and can modulate the response to immunotherapy. Preclinical studies have shown that specific gut microbes and their metabolites, such as short-chain fatty acids (SCFAs) and tryptophan metabolites, can enhance immunotherapy efficacy by improving immune cell function and tumor infiltration. Human studies have also identified associations between gut microbiome composition and immunotherapy outcomes, with certain bacterial taxa linked to better responses to ICIs. Microbiome-targeting approaches, such as fecal microbiota transplantation (FMT), probiotics, and prebiotics, are being explored to enhance immunotherapy. These interventions aim to modulate the gut microbiome to improve immune responses and reduce adverse events. However, challenges remain in standardizing protocols, ensuring safety, and understanding the underlying mechanisms. Current research emphasizes the need for large-scale, longitudinal studies and multidisciplinary collaboration to fully understand the role of the gut microbiome in cancer immunotherapy. Advances in sequencing technologies and engineered bacteria offer new opportunities to develop more effective microbial interventions. Future directions include standardizing protocols, improving safety, and exploring novel strategies to enhance immunotherapy outcomes through microbiome modulation.The gut microbiome plays a critical role in cancer immunotherapy, influencing treatment efficacy and patient outcomes. Immunotherapy, particularly immune checkpoint inhibitors (ICIs), has shown promise in cancer treatment, but its effectiveness varies among patients. The gut microbiome, including bacteria, viruses, and fungi, interacts with the immune system and can modulate the response to immunotherapy. Preclinical studies have shown that specific gut microbes and their metabolites, such as short-chain fatty acids (SCFAs) and tryptophan metabolites, can enhance immunotherapy efficacy by improving immune cell function and tumor infiltration. Human studies have also identified associations between gut microbiome composition and immunotherapy outcomes, with certain bacterial taxa linked to better responses to ICIs. Microbiome-targeting approaches, such as fecal microbiota transplantation (FMT), probiotics, and prebiotics, are being explored to enhance immunotherapy. These interventions aim to modulate the gut microbiome to improve immune responses and reduce adverse events. However, challenges remain in standardizing protocols, ensuring safety, and understanding the underlying mechanisms. Current research emphasizes the need for large-scale, longitudinal studies and multidisciplinary collaboration to fully understand the role of the gut microbiome in cancer immunotherapy. Advances in sequencing technologies and engineered bacteria offer new opportunities to develop more effective microbial interventions. Future directions include standardizing protocols, improving safety, and exploring novel strategies to enhance immunotherapy outcomes through microbiome modulation.