Silica/polyurea hybrid microcapsules loaded with hexamethylene diisocyanate (HDI) as core materials were prepared via a combined strategy of interfacial polymerization and an in situ sol–gel process in an oil-in-water emulsion. They were clearly characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. The resultant microcapsules have diameters of 57–328 μm, shell thicknesses of 1–8 μm, and core fractions of 51.2–65.6%. The diameter and shell thickness were linearly related to the agitation rate in the double logarithm coordinates, and the core fraction were linearly related to the agitation rate, indicating that the structure and component of the microcapsules can be controlled effectively. The resistant properties against thermal and solvent attacks were assessed by using thermogravimetric analysis and titration. The results show that the microcapsules had outstanding thermal stability with initial evaporation temperature (defined at 5% of weight loss), increased by around 58 °C compared with that of pure core material, and good resistance to xylene with less than 25.9 ± 0.7 wt% reduction of core content after immersion for 100 h. Self-healing anticorrosion coatings based on microcapsules were fabricated on a steel substrate. Preliminary results indicated significant corrosion retardancy occurred in the coatings under an accelerated corrosion process, showing the great potential of our microcapsules in the development of catalyst-free, one-part, self-healing coatings for corrosion control.