Poly(N-isopropylacrylamide) (PNIPAAm)/calcium carbonate (CaCO3) micro/nanohybrid composites with smart drug-delivery property had been prepared via in situ biomineralization reaction. Sodium poly(styrene sulfonate) (PSS) was used as the crystal growth additive to control the crystalline polymorph of CaCO3 and the morphology of the hybrid materials. The interaction between PSS and Ca2+ contributed to the formation of hierarchical micro/nanohybrid composites, in which microscale vaterite microparticles were covered by nanoscale PNIPAAm micelle. Vitamin B2 (VB2) release behavior was found to be pH- and thermal-responsive. Moreover, the release profiles were sustained with the introduction of CaCO3 microparticles, suggesting that CaCO3 microparticles could hinder the permeation of the encapsulated VB2 and reduce the drug release effectively. The prepared micro/nanohybrid materials can be used as smart hierarchical materials for controlled drug delivery. (c) 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013