This paper demonstrates a proof-of-concept approach for encapsulating the insulin and Fe3O4 nanoparticles into size-controllable alginate microcapsules utilizing the electrostatic droplets (ESD) technique. We have established that the combination of ESD and external gelation is quite effective in producing uniform-sized polymer particles. In addition, using the external gelation technique, the droplets containing a sodium-alginate were gelled in situ by immersion in Ca2+, Ba2+, or Cu2+ ions for a few minutes. The results show that different-type divalent cations caused various surface features to appear on the microcapsules (e.g., cracking, orange peel, pitting, splitting, wrinkling, etc.). The particle size can be adjusted from a few micrometers to ca. 1,000 μm by electrostatic force. The microcapsules can be made magnetic by incorporating a super-paramagnetic nanomaterial (e.g., Fe3O4 nanoparticles) during the preparation. The composite magnetic microcapsules are potential candidates for a magnetic-responsive drug delivery system. In addition, our results show that the encapsulation and in vitro release of a model drug, insulin, can enhance the effect of the controlled release. These microcapsules are addressable by an external magnetic field and are capable of loading a model drug and releasing it in a highly differential drug release profile. We have demonstrated that the appropriate magnetic field intensity for different release patterns is predictable, which enables a better application of microcapsules as a smart drug carrier.