Various nanomaterials have been developed for biomedical applications, which can be classified into organic, inorganic, and organic–inorganic hybrid nanomaterials. Peptide-based nanomaterials have demonstrated unique functions and advantages in tumor diagnosis and therapy, such as specific tumor targeting for accurate tumor diagnosis and excellent tumor selectivity for efficient tumor therapy. Moreover, peptides can be easily integrated into a variety of different nanomaterials to develop superior integrated multifunctional nanomaterials for tumor diagnosis and therapy. Therefore, the peptide-based multifunctional nanomaterials will greatly promote the development of antitumor research and further enhance the transformation from scientific research to clinical applications.