The effect of minor addition of antimony (Sb) and rare earth metal (REE) on microstructure and mechanical properties in the ductile cast iron (FCD450, (JIS G5502)), especially the morphology of spheroidal graphite, were investigated by TEM technique for TEM samples prepared by a focused ion beam (FIB) method. The increasing of amounts of Sb increased strength and hardness, and decreased elongation and impact absorption energy of alloys. The mean size of spheroidal graphite decreased, while the area fraction of pearlite increased with increasing amount of Sb. The alloy including 0.1%Sb had a spheroidal graphite which shows a smooth surface and clear sphere. The thin foil was sectioned from this spherical graphite by FIB method and observed by transmission electron microscope. This spheroidal graphite consisted of annular layers which was indexed as the graphite structure based on the analysis of SAED patterns. The addition of REE to this alloy did not affected on its mechanical properties and microstructure in the present work.