Carboxylated acrylonitrile-butadiene rubber (CNBR)-clay mixtures were prepared by co-coagulating rubber latex and clay aqueous suspension, then combining the mixtures with a rubber ingredient and vulcanizing by a traditional rubber mixing processing procedure. Transmission electron microscopy (TEM) showed that the silicate layers of clay were delaminated or intercalated with CNBR and dispersed in the CNBR matrix at a nanometer level during co-coagulating. X-ray diffraction indicated that the amount of CNBR intercalating between the layers increased with the increase of content of clay in CNBR, which is in contrast with the results of other studies. Some reasons were put forward for this discrepency. The aspect ratio (width/thickness) of the platelet inclusions was reduced and the silicate layers were aligned more orderly during the compounding operation on an open mill. The intercalated CNBR, on co-coagulating, still remained within the interlayer space after curing. In these nanocomposites, the particles of silicate layers were dispersed at the nanometer level and the structure was a combination of delaminated and intercalated silicate layers dispersed in the continuous CNBR matrix.