Robust poly(urea-formaldehyde) (PUF) microcapsules with composite shells comprising zirconia (ZrO2) nanopowder incorporated in PUF were fabricated via a novel and facile one-pot synthesis. ZrO2 nanopowder was chosen because it owns one of the highest mechanical strengths among ceramics. The nanopowder was predispersed in the core material to combine encapsulation and fortification into a single process. In the core, the well-dispersed nanopowder migrated to the interface, where PUF polymerization took place. The mechanical strength of the microcapsule with nano-ZrO2 incorporated in the shell (42% by weight) is three times greater than that of the microcapsule without ZrO2. In a preliminary application wherein the microcapsules were embedded in a model of poly(vinyl alcohol) (PVA) membrane, the PVA specimen exhibited a higher ultimate tensile strength when fortified microcapsules were embedded than when unfortified microcapsules were used.