Natural rubber (NR)-clay (clay is montmorillonite) and chloroprene rubber (CR)-clay nanocomposites were prepared by co-coagulating the rubber latex and clay aqueous suspension. Transmission electron microscopy showed that the layers of clay were dispersed in the NR matrix at a nano level, and the aspect ratio (width/thickness) of the platelet inclusions was reduced and clay layers aligned more orderly during the compounding operation on an open mill. However, X-ray diffraction indicated that there were some nonexfoliated clay layers in the NR matrix. Stress-strain curves showed that the moduli of NR were significantly improved with the increase of the amount of clay. At the same time, the clay layers inhibited the crystallization of NR on stretch, especially clay content of more than 10 phr. Compared with the carbon-black-filled NR composites, NR-clay nanocomposites exhibited high hardness, high modulus, high tear strength, and excellent anti-aging and gas barrier properties. Similar to NR-clay nanocomposites, CR-clay nanocomposites also exhibited high hardness, high modulus, and high tear strength. (C) 2005 Wiley Periodicals, Inc.