Core/shell structured nanoparticles (NPs) are a novel category of functional materials that have garnered widespread attention due to their advantageous preparation methods, unique characteristics, and multifunctional application prospects, which have shown significant performance in materials chemistry and many other fields, such as electronics, biomedical, pharmaceutical, optics, and catalysis. Although some reviews about core/shell NPs have been published, there is still an intense requirement for an extensive review about the updated literature and new reported core/shell nanomaterials. Colloidal quantum dots (QDs) and noble metal NPs have a very small size, which results in the large surface-to-volume ratio and under-coordinated chemical bonds. As a result, the effort on the design of core-shell structure has been essential for colloidal QDs and noble metal NPs. In this review, the core-shell structures dominated by traditional QDs and CsPbX perovskite QDs, as well as noble metal nanocrystals (NCs) were summarized. The applications of the above core-shell structure NCs in medical or biological fields such as sensing, biological imaging, medical diagnostics and therapeutics, immunological diagnosis were discussed. The main objective of this review is to provide a better basis for the synthesis, properties, and biomedical applications of QDs or noble metal core/shell NPs, which is beneficial for the further development of QDs, noble metal NPs, and other NPs.