The mechanical and thermal characteristics and morphology of polyamide 6 (PA6)/isotactic polypropylene (iPP) blends (10/90 w/w) prepared with different processing procedures and incorporated with an aryl amide nucleating agent, a kind of beta-nucleating agent (beta-NA) for iPP, were investigated. The yield strength and flexural modulus of the blends decreased as beta-NA was introduced into the blends, whereas the impact strength and elongation at break improved. The crystalline structures of the blends closely depended on (1) the processing conditions and (2) competition between the beta-nucleating effect of beta-NA and the alpha-nucleating effect of PA6 for iPP. Scanning electron microscopy, differential scanning calorimetry, and X-ray diffraction were adopted to reveal the microstructures of the blends. At a low beta-NA content (< 0.1 wt %), the alpha-phase iPP dominated the blends, whereas the relative content of the beta-phase iPP increased remarkably when the beta-NA content was not less than 0.1 wt %. The processing conditions also showed profound influences on the supermolecular structures of iPP; this resulted in different mechanical properties of the blends. As for PA6, the crystallization behavior and crystalline structure did not exhibit obvious changes, but PA6 did play an important role in the epitaxial crystallization of iPP on PA6. (c) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 121: 554-562, 2011