An emerging focus in nanomedicine is the exploration of multifunctional nanocomposite materials that integrate stimuli-responsive, therapeutic, and/or diagnostic functions. In this effort, cysteine-rich proteins have drawn considerable attention as a versatile platform due to their good biodegradability, biocompatibility, and ease of chemical modification. This review surveys cysteine-rich protein-based biomedical materials, including protein-metal nanohybrids, gold nanoparticle-protein agglomerates, protein-based nanoparticles, and hydrogels, with an emphasis on their preparation methods, especially those based on the cysteine residue-related reactions. Their applications in tumor-targeted drug delivery and diagnostics are highlighted.