Poly(vinyl chloride)/layered double hydroxides (PVC/LDHs) composite resins were prepared by in sitti suspension polymerization of vinyl chloride monomer in the presence of LDHs intercalated with dodecyl sulfate anions (LDH-DS), and were further processed to obtain PVC/LDH-DS nanocomposites. It was found that the mean particle size of PVC composite resins decreased as LDH-DS was added in the polymerization system. The 5 and 10% weight loss temperatures of PVC resins significantly increased with the increase of LDH-DS weight fraction in the composite resins. The transmission electron microscopy images showed that LDH-DS particles were partially intercalated and partially exfoliated, and well distributed in the PVC nanocomposites. The storage modulus below the glass transition region and the glass temperature of the PVC/LDH-DS nanocomposites are greater than that of the pristine PVC. The mechanical properties of PVC/LDH-DS nanocomposites indicate that LDH-DS nanoparticles stiffen and toughen PVC. The tensile strength, Young's modulus, and Charpy notched impact strength of the PVC/LDH-DS nanocomposites are greater than those of the pristine PVC and PVC/LDH-DS composites prepared by the melt blending. (c) 2006 Wiley Periodicals, Inc.