The mechanical properties and crystal morphological structures of dynamically photocrosslinked polypropylene (PP)/ethylene-propylene-diene terpolymer (EPDM) blends have been studied by mechanical tests, wide-angle X-ray diffraction (WARD), scanning electron microscopy (SEM), and differential scanning calorimetry (DSC). Dynamically photocrosslinking of PP/EPDM blends can improve the mechanical properties considerably, especially the notched Izod impact strength at low temperature. Data obtained from mechanical tests show that the notched Izod impact strength of a dynamically photocrosslinked sample with 30% EPDM at -20 degreesC is about six times that of an uncrosslinked sample with the same EPDM component. The results from the WARD, SEM, and DSC measurements reveal the enhanced mechanism of impact strength for the dynamically photocrosslinked PP/EPDM blends as follows: (i) the beta-type crystal structure of PP is formed and the interplanar distance of alpha-type crystal increases slightly with an increase in the EPDM component; (ii) the droplet size of the EPDM phase in the photocrosslinked PP/EPDM blends is obviously reduced and the droplet number is increased with an increase in the EPDM component during the dynamical photocrosslinking process; (iii) the graft copolymer of PP-g-EPDM is formed at the interface between PP and EPDM components. All the above changes from the crystal morphological structures are favorable for increasing the compatibility and enhancing the toughness of PP/EPDM blends at low temperatures.