Electrospun polymer micro/nanofibers have been widely explored as platforms for controlled delivery of therapeutic agents. Electrospun fibers are featured by large surface area, high porosity, and tunable morphology, which can be manipulated to fabricate micro/nanofibers with appropriate physicochemical properties, degradation kinetics, and drug release profiles. Many therapeutic agents can be separately or simultaneously loaded by electrospun fibers in the application of cancer therapy, adhesion prevention, wound repair, and regeneration of bone and nerve. In this review, we mainly introduce the basic principles of electrospinning, and the mechanisms and applications of electrospun micro/nanofibers for delivery of small molecule drugs, proteins, and nucleic acids in the healthcare field.