The polymorphic compositions and mechanical properties of isotactic polypropylene (iPP) samples nucleated by a selective beta-nucleating agent [N,N'-diphenyl adipamide (DPA)] were investigated with wide-angle X-ray diffraction, polarized light microscopy, scanning electron microscopy, and mechanical tests. It Was found that beta-phase crystals emerged with the addition of DPA, and the relative proportion of the beta-crystalline form reached the maximum Value of 0.97 with the addition of 0.1 wt % DPA. The curved lamellae in the beta spherulites were like flowers. The beta spherulites were etched more easily than alpha spherulites because amorphous regions were distributed inside the beta spherulites The Izod notched impact strength increased sharply with the addition of DPA and attained the maximum value of 7.30 kJ/m(2) (the Value of blank iPP was 3.13 kJ/m(2)) with the addition of 0.1 wt % DPA. An analysis of the misfit factors between DPA and beta-iPP showed that beta-iPP could epitaxially crystallize on the DPA crystal well. (C) 2008 Wiley Periodicals, Inc. J Appl Polym Sci 111: 1738-1744, 2009