Relationships among rheological properties of polypropylene/rubber/talc (PP) alloys, process conditions of injection molding and tiger-striped flow marks appeared in the injection moldings of PP alloys have been investigated. The three PP alloys used in this study consisted of ethylene propylene block copolymer (EPBC), ethylene butene rubber (EBR) and talc. From the visual observation and the luminance change of the reflected image of the slit light, the flow marks of the injection moldings were evaluated. Although we were able to confirm the appearance of flow marks, there was something inconspicuous. It was found that the injection speed region or the shear rate region of the flow front where the flow marks were inconspicuous differed depending on the materials. The relation between the characteristic shear rate which is the product of the shear rate and the relaxation time and the flow mark was investigated. As a result, if the characteristic relaxation time was more than 100, the occurrence of flow marks was suppressed regardless of the materials. On the other hand, if the characteristic relaxation time was less than 50, flow marks occurred but became inconspicuous. We also propose improvement methods for tiger stripe flow mark of PP alloy.