This study aims to explore the joint effects of specific P-nucleation and rubber dispersion on morphology and mechanical behavior of materials derived from isotactic polypropylene. A beta-nucleator (N,N'-dicyclohexylnaphthalene-2,6-dicarboxamide) and an amorphous EPM rubber were used for the modification of isotactic polypropylene. Four samples were investigated: neat polypropylene, the same polymer modified with 0.03 wt% of beta-nucleator or with 15 wt % of dispersed rubber particles, and finally polypropylene containing both the beta-nucleator and the rubber particles. Tensile and impact behavior were followed at room and cryogenic temperatures. It has been observed that the beta-nucleation and rubber modification have brought about a similar macroscopic softening effect on the tensile mechanical behavior. Microscopy of fracture surfaces, however, has shown different toughening mechanisms caused by specific nucleation on one hand and by rubber dispersion on the other. While a distinct synergy effect of nucleation and rubber modification on the resulting toughness was found at low temperature, no such cooperative effect manifested itself at room temperature. (c) 2006 Wiley Periodicals, Inc.