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