Mechanical properties of cast irons are mainly determined by two factors of microstructures, graphite forms and matrices. Both graphite forms and matrices affect electromagnetic properties very complicatedly. The authors have investigated electromagnetic properties of flake graphite cast irons and ductile cast irons in relation to the their microstructures, and applied electromagnetic nondestructive evaluation method such as eddy current method and DC potential drop method to characterize microstructures of various kind of cast irons. In this paper, we review relationship between electromagnetic properties and microstructures. Issues discussed include ferrite and pearlite ratio in ductile cast irons which decides the hardness, and graphite forms in fake graphite cast irons which is important to estimate damping and wear properties of flake graphite cast irons. Finally, we discuss feasibilities of some applications of electromagnetic nondestructive evaluation methods to characterize graphite forms and matrices of cast irons.