Abstract: Immune checkpoint inhibitors (ICIs) have emerged as critical agents in cancer immunotherapy; however, their resistance and limited response in most patients pose significant challenge. The gut microbiota, as a pivotal immune regulator, has been increasingly recognized for its role in enhancing the therapeutic efficacy of ICIs. Studies demonstrate that fecal microbiota transplantation or transplantation of specific bacterial strains can directly reshape the gut microbiota composition, thereby improving ICI therapeutic outcomes. Furthermore, dietary interventions, prebiotics, and postbiotics have shown potential in augmenting the anti-tumor effects of ICIs through gut microbiota modulation. Despite these promising findings, further investigations are required to optimize microbiota-based strategies and therapeutic protocols. This review highlights the critical role of gut microbiota modulation in ICI-based cancer therapy and explores its clinical applications, offering both practical insights and theoretical foundations for improving immunotherapy outcomes against various cancers.