 Metal organic frameworks, MOFs, have attracted much attention in recent years due to their unique properties and advantages as nanocarriers for drug delivery and biomedical applications, including well-defined structure, ultra-high surface area and porosity, tunable pore size, and easy chemical functionalization. State-of-the-art strategies to functionalize MOFs with therapeutic agents were summarized, including surface adsorption, pore encapsulation, covalent binding, and functional molecules as building blocks. The most recent biological applications of MOFs for intracellular delivery of drugs, proteins, and nucleic acids, especially aptomers, were presented. Challenges and prospects were comprehensively discussed to provide context for future development of MOFs as efficient drug delivery systems. This article is authored by Yu Jia-sun, Li Weijing, Yu Yang, and others.