Abstract: In recent years, immunotherapy, as an emerging anti-tumor therapy, has shown great potential in the treatment of both solid and hematologic tumors. There is increasing preclinical and clinical evidence linking the composition of gut microbiome with the efficacy as well as adverse effects of immune checkpoint inhibitor anti-tumor therapy. We summarized in this review the modulatory role of the gut microbiome in antitumor therapy with different immune checkpoint inhibitors. We also discussed the limitations of existing research and prospective development of the further clinical strategies.