In this work, a one-pot route to prepare emulsions of silica/polymer core-shell composite particles was developed through the direct sol–gel processing of alkoxysilane on the surface of newly synthesized template polymer particles in emulsifier-involved aqueous emulsions. It included two continuous steps: first, the polymer emulsions were synthesized through emulsion polymerization, and second, the template particles in the emulsions were directly coated with silica via sol–gel reaction of precursors without adding ethanol or removing emulsifiers. The size and morphology of the composite particles were characterized, and the results showed that the silica/polymer composite particles with core-shell structure could be prepared only on the basis of cationic template emulsions, and the in situ-coating reaction of sol–gel precursors carried on easier with the increasing of the positive charge density on the surface of template particles. The films formed from the composite emulsions were found to have superior optical and flame-retardant properties compared to polymer films, owing to the core-shell composite microstructure of the particles.