The variations in the microstructure and tensile properties of dual-matrix ductile irons have been investigated non-destructively by Magnetic Barkhausen Noise (MBN) method. Specimens have been intercritically austenitised at 795 degrees C and 815 degrees C for 20 minutes, and then oil-quenched to obtain different martensite volume fractions. Two specimens, namely as-cast and oil-quenched from 900 degrees C, were prepared for comparison purpose. To investigate the effect of tempering, some specimens were tempered at 500 degrees C for 1 h and 3 h. The results showed that there is a good correlation between MBN response and variations in microstructure and mechanical properties. The volume fraction of martensite can be controlled to modify the mechanical properties, and all changes in the microstructure can be nondestructively monitored by MBN.