Isotactic polypropylene (PP) with MFIs of 0.43 to 44.5 g/10 min were added with 0 to 10 ppm of gamma-quinacridone, a beta-crystal nucleator of PP. Flexural test specimens were injection-molded from the PPs at constant molding conditions and the structures and properties have been studied. 1) The crystallization temperature increases with gamma-quinacridone content and MFI of the base resin. 2) The beta-crystal content increases with gamma-quinacridone content and MFI. 3) The thickness of the skin layer decreases with MFI and scarcely depends on gamma-quinacridone content. 4) The orientation of beta-crystals decreases with MFI. 5) The Izod impact strength increases with gamma-quinacridone content for PP with MFI < 40 g/10 in, and decreases with MFI. However, little improving effect of gamma-quinacriclone is observed for MFI > 40 g/10 min. 6) The flexural modulus and stlength decreased by about 10 to 20 % by the addition of gamma-quinacridone and the decrease is more significant for PP with higher MFI. 7) The heat distortion temperature increases with gamma-quinacridone content and the increase becomes more prominent with increasing MFI. 8) The mold shrinkage increases with gamma-quinacridone content and decreases with MFI.