Montomorillonite was organically modified with three different swelling agents: n-dodecylamine, 12-aminolauric acid, and 1,12-diaminodecane. These organoclays and polyamide 6 (PA6) were blended in a formic acid solution. X-ray diffraction analysis showed that the clay still retained its layer structure in the PA6/clay nanocomposite. Consequently, these materials were intercalated nanocomposites. The effects of the swelling agent and organoclay content on the crystallization behavior of the PA6/clay nanocomposites were studied with differential scanning calorimetry. The results showed that the position and width of the exothermic peak of the PA6/clay nanocomposites were changed during the nonisothermal crystallization process. The clay behaved as a nucleating agent and enhanced the crystallization rate of PA6. The crystallinity of PA6 decreased with an increasing clay content. Different swelling agents also affected the crystallization behavior of PA6. The effects of the type and content of the swelling agent on the tensile and flexural properties of PA6/clay nanocomposites were also investigated. (C) 2003 Wiley Periodicals, Inc.