The structure development and mechanical properties of blow extruded polypropylene containing beta-phase nucleating additives was studied. Quinacridone red and cadmium red were both found to nucleate the beta phase in polypropylene, the former being a much more efficient nucleator than the latter. The beta-phase spherulites formed in the presence of these nucleating agents were small and extensively volume filled, yielding high crystallinity. The modulus increased 2-3 times, elongation at break decreased, and there was a sharp break point without much yield when the beta-phase nucleating agents were added as compared to the pure alpha-phase polypropylene.