Molecular self-assembly is ubiquitous in nature lives. As peptides are the basic building block of proteins to create fascinating functions in nature, the pharmacological activity of their self-assembly has ushered in a new era in the drug design and delivery. As a bottom-up method, the self-assembly is a powerful way to create higher-order structures from monomer at the nanoscale to supramolecular at the microscale, creating diverse materials that integrate different functional properties. By harnessing controllable self-assembly processes, peptide-modified nanomedicines can achieve site-specific responsiveness within tumor regions. The nanostructural modifications can also enhance the drug retention for the tumor cell elimination or enable size-variable delivery strategies. This synergistic approach to the peptide self-assembly enables tumor-targeted therapy with reduced side effects and has great potential for clinical application.