Polyamide 6/Na+ montmorillonite (Na+ MMT) nanocomposites (NCs) were produced in a corotating twin screw extruder. Water was injected into the extruder as an intercalating/exfoliating agent. The wide angle X-ray diffraction and linear dynamic measurements were used to investigate the structure of the prepared samples. The results showed that the contact time between water and melt PA6/Na+MMT in the extruder is an important factor to achieve a high level of exfoliation. The ratio of water-injection rate to clay feeding rate did not reveal a major effect on the exfoliation of pristine MMT. The results also demonstrated that the order of injection of water during the mixing process did not have a distinguishable effect on the level of exfoliation. This processing method was found to be controlled by a diffusion mechanism caused by the presence of water molecules during the process. Improvement of tensile properties is in a great agreement with the rheological and morphological findings. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 119: 736-743, 2011