Data published so far and some results obtained in the author's laboratory are outlined. Spheroidization of graphite in iron can be achieved in the wide range of composition: C 2.4-4.2%, Si 0.8-6.0%, Mn 0-1.0%, P<1.0%, S<0.2%, although Mn<0.4%, P<0.05% and Si 2.0-3.5% are needed for the high ductility of the iron as cast. The total carbon content must be 3.5% plus in order to avoid the high shrinkage in casting, but C 4.0% plus sometimes causes the flotation of graphite in massive castings. The less the sulphur content is, the easier the spheroidization becomes.In irons treated with magnesium, it is probably adsorbed on the surface of the graphite nodules precipitated from melt, but the binding condition of Mg atoms in irons obtained by tempering the white irons of the same melt differs from that in nodular irons as cast.The chemical, physical and mechanical properties are varied in the wide range by the chemical composition and the microstructure of the ground mass embeded with the spheroidal graphite. The irons are stronger and tougher than the ordinary gray iron, and have generally both markedshock resistance and heat resistance.