A homo isotactic polypropylene (PP) and random and block PP copolymers with ethylene were added with 0 to 10 ppm of gamma-quinacridone which is a beta-crystal nucleator of PP. Flexural and Izod impact test specimens were injection-molded from the PPs at cylinder temperatures of 200 to 320 degrees C and the structure and properties have been studied. 1) Although the beta-crystal content of the block PP is nearly the same as that of the homo PP, the beta-crystal content of the random PP is largely lower than that of the homo PP. 2) The Izod impact strength is increased by the addition of gamma-quinacridone. The increase is high for the homo and block PPs and very low for the random PP. There are cases where the Izod impact strength is increased by more than four folds for the block PP. 3) The flexural modulus and strength are decreased by the addition of gamma-quinacridone and the decreases of the random PP are lower than those of the homo and block PPs. From above, it may be said that the modification effect of PP by the addition of gamma-quinacridone is prominent for the homo and block PPs in which the beta-crystal is ease to form and the effect is weak for the random PP in which the beta-crystal is difficult to form.