Zeolitic imidazolate framework-8(ZIF-8) is a class of porous crystalline materials formed by the self-assembly of zinc ions and 2-methylimidazole. It shows potential advantages in encapsulation and transportation of functional materials owing to its high porosity, large specific surface,convenient synthesis and controllable size. More importantly, ZIF-8 is an ideal carrier for drug delivery and release due to its excellent biocompatibility, stability under physiological conditions and responsiveness to the weak acidic environment associated with malignant tumors and other diseases. In fact, the small molecular drugs(doxorubicin, 5-fluorouracil) and biological macromolecules(antibody, nuclein) have all been loaded into ZIF-8 for chemotherapy, photothermal therapy, photodynamic therapy and biosensing. The particle size of ZIF-8 is very important for biomedical applications, and accurate functional regulation of ZIF-8 is agreat challenge for its biomedical application. Herein, we review the synthesis methods, size-control and biomedicalapplications of ZIF-8.