Communication: CaCO3/polystyrene inorganic/organic composite nanoparticles (50 nm) with a core/shell structure were synthesized in 80% yield by emulsion polymerization. Nanometer CaCO3 was pretreated with gamma -methacryloxypropyltrimethoxysilane in order to introduce polymerizable groups onto its surface. Soxhlet extraction experiments have shown that only 4% of total encapsulating polystyrene (PS) was removable when the ratio of CaCO3 to styrene was relatively low (14.8-29.6%), indicating strong adhesion between CaCO3 and PS.