A structural design featuring rattle-type silver/titania (Ag/TiO2) core/shell, that is, Ag@TiO2, composite microcapsules is produced. The TiO2 shell protects the encapsulated, movable Ag nanoparticles from breaking away under moderate loading, minimizing hence adverse environmental and biological exposure due to the metal loss, whereas the mesoporous shell serves as conduits for Ag ions released from the caged Ag nanoparticles to kill Escherichia coli in aqueous solutions under dark condition. The anatase TiO2 shell imparts an additional, synergistic photocatalysis activity under ultraviolet irradiation. A pronouncedly enhanced photocatalysis activity results when the Ag@TiO2 composite capsules were thermally annealed under vacuum. This “rattle-in-ball” hybrid architecture enables bifunctional bactericide and photocatalysis capability under both light and dark conditions, as well as mitigated environmental and biological impact in practical use.