Nucleation characteristics of isotactic polypropylene (iPP) nucleated by the alpha/beta compounded nucleating agents (NAs) were investigated by wide-angle X-ray scattering, differential scanning calorimetry and mechanical testing. The results showed that the nucleation effect of the a/b compounded NAs depends on not only nucleation efficiency (NE) of individual beta and alpha NAs and their ratios but also the processing conditions, especially the cooling rates. The nucleating characteristics of the alpha/beta compounded NAs can be illustrated by competitive nucleation. The NA with high NE played a leading role during iPP crystallization even at a low weight ratio and at different cooling rates. The stiffness and toughness of iPP can be simultaneously improved by using suitable compositions at the appropriate ratios. Finally, the nonisothermal crystallization kinetics of iPP nucleated with the alpha/beta compounded NAs was described by Caze method and the crystallization activation energy of nucleated iPP was calculated by Kissinger equation. The result indicated that the crystal growth pattern of nucleated iPP was heterogeneous nucleation followed by three-dimension spherical growth. (C) 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 653-665, 2010