We report a potential example of using surface functionalization to provide magnesium alloys (Mg–Ca) with controlled release and corrosion resistance properties. A key feature of this approach is to treat the Mg–Ca surfaces with nanoparticles via electrodeposition that can stably load and controllably release bioactive agents or drugs. These photo-cross-linkable and nano-scale particles were prepared by the self-assembly of an amphiphilic poly(γ-glutamic acid)-g-7-amino-4-methylcoumarin (γ-PGA-g-AMC) with encapsulation of a vitamin; moreover, the size and morphology of the resulting particles were studied. Fluorescence microscopy analysis indicated that Vm was effectively incorporated into the γ-PGA-g-AMC particles. Scanning electron microscopy (SEM) images showed that the colloidal particles could be uniformly electrodeposited on the Mg–Ca alloys. Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) analyses confirmed the successful anchoring of the particles. After the surface electrodeposition of self-assembled colloidal particles, the in vitro degradation results show that deposition of the particles was found to reduce the degradation rate of the magnesium alloys; moreover, the vitamin was controllably released for up to 20 days. Furthermore, the Mg–Ca substrate functionalized with colloidal particles containing a vitamin significantly promoted the attachment, proliferation and spread of NIH-3T3 normal cells. The entire strategy may be used in various medical devices to create coatings for improved biomedical performance.