An isotactic polypropylene homopolymer (PP) was added with 0 to 10000 ppm of gamma-quinacridone, a beta-crystal nucleator of PP. Flexural test specimens were injection-molded from the PP at cylinder temperatures of 200 to 320 degrees C and the structures and properties have been studied. The results can be summarized as follows: The crystallization temperature increases with gamma-quinacridone content. The beta-crystal content decreases with increasing cylinder temperature and shows a maximum at a gamma-quinacridone content of about 100 ppm. The thickness of the skin layer scarcely depends on gamma-quinacridone content. The orientation of beta-crystals decreases with increasing cylinder temperature. It is high at the surface regions and decreases toward the interior. The Izod impact strength increases with gamma-quinacridone content. The degree of the increase is higher as the beta-crystal content is higher and reaches move than threefold in the highest case. The flexural modulus and strength decrease by about 10% in the highest case. The heat distortion temperature increases with gamma-quinacridone content. The mold shrinkage increases with gamma-quinacridone content. From these results, it is concluded that the injection moldings of PPs containing gamma-quinacridone are superior in impact strength and heat resistance.