The objective of this work is to understand the effect of shear force on the properties of epoxy-clay nanocomposites. The shear force was controlled by changing the revolutions per minute on a mechanical mixer. Differences in the aspect ratio of clay layers and differences of clay particle distribution in the epoxy matrix were caused by shear force. Shear force mechanism on epoxy-clay nanocomposites' intercalation/exfoliation were compared with the other mechanism already suggested. X-ray diffraction, transmission electron microscopy, and scanning electron microscopy were utilized to investigate the degree of exfoliation and morphology. The mechanical and thermal properties were also studied to demonstrate the effect of shear force. This study revealed that appropriate shear force and mixing time on nanocomposite preparation was required to achieve the desired properties. (c) 2006 Wiley Periodicals, Inc.