Abstract: Immunotherapy has emerged as the most widely used cancer treatment strategy. Immune checkpoint blockade, cell therapy, and tumor vaccines have all achieved remarkable progress in clinical trials. Over recent years, monoclonal antibodies and peptide drugs have gained increasing attention as representatives for immune checkpoint blockades. This review summarized the research progress and application of peptide drugs targeting immune checkpoints, including single-target peptide blockers, bifunctional peptide blockers, and self-assembled peptides, as well as the application of peptides targeting immune checkpoints in cancer diagnosis. In addition, we offer new ideas to the bottleneck faced by peptide drugs for application in cancer immunotherapy.