Several composites of a metallocene syndiotactic polypropylene with an organophilic silicate have been prepared and analyzed to investigate the effects of the nanoparticles on the crystallization of syndiotactic polypropylene. Moreover, the influence of an electron-irradiation dose of 166 kGy on the different materials has been studied. Although the melting temperatures are practically unchanged, irradiation leads to a considerably slower crystallization rate of the syndiotactic polypropylene homopolymer in such a way that an important cold crystallization has been observed in the second melting along with a much higher value of the isothermal crystallization half-time. On the contrary, the nanocomposites are much less sensitive to irradiation because only a small shift of the crystallization temperature has been observed, and the isothermal crystallization half-time remains practically unaffected. However, irradiation leads to important changes in the low-angle region of X-ray diffractograms. (c) 2007 Wiley Periodicals, Inc.