In elastomer/organo clay nanocomposites, the morphological characteristics, and hence the mechanical properties, of the vulcanizates are strongly influenced by the organic modifier and the vulcanization process. When the elastomer itself undergoes strain-induced crystallization, both the organic modifier and the dispersed filler particles could significantly influence the crystallization process. These phenomena are very common in case of natural rubber-based vulcanizates. In this study, the similar effects have been demonstrated with carboxylated nitrile rubber (XNBR) and organically modified layered double hydroxide (O-LDH)-based nanocomposites. The effect of size of the organic modifier was obviously visible on the interlayer distance of O-LDH and also on the morphological reorganization of the dispersed O-LDH particles during vulcanization process. The strain-induced crystallization of the XNBR was found to be strongly dependent on the morphological change that occurs during vulcanization process. (C) 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 2302-2311, 2010