Sintered parts can be mass-produced with high precision and cost-effectiveness, and have a wide range of applications, including in automobiles. Since conventional sintered materials tend to show lower fatigue strength than that of wrought steel, they cannot be applied to high load applications.The effect of homogeneity in the microstructure of sintered materials on fatigue strength has been investigated in many studies. In this paper, we compare fatigue strength between homogeneous and heterogeneous materials. Our study reveals that in a high-density range of about 7.7 g/cm³, cracks occur at the surface starting point, and homogeneous materials have a fatigue life 10 times longer than that of heterogeneous materials.