Poly(vinyl chloride) (PVC)-based nanocomposites containing calcium carbonate nanoparticles (CaCO3) were prepared. Different nanoparticle surface modifiers were selected and tested to promote matrix/filler interactions and, consequently, to obtain high-performance materials. In particular, the nanoparticles were modified with poly(acrylic acid) (PAA) and poly (butadiene-co-acrylonitrile-co-acrylic acid) (PBAA). For comparison, PVC-based materials, with the addition of commercial neat and stearic acid modified CaCO3, were also prepared. The influence of CaCO3 and surface modifiers on the gelation, thermal properties, thermal stability, and mechanical properties of PVC was studied. The gelation time of the rigid PVC/CaCO3 composites decreased as a function of the percentage and surface treatment of CaCO3. Morphological analysis proved the effectiveness of PAA and PBAA as surface modifiers; they obtained for the corresponding materials a typical nanostructured morphology. A significant improvement in the PVC thermal stability was recorded with the addition of neat and stearic acid modified CaCO3. Finally, mechanical tests showed an increase in the flexural strength and toughness of PVC as a function of the nanoparticle surface modifier. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 122: 3590-3598, 2011