In this study, we investigated effect of Mo addition on mechanical properties of Cu added ADI. Ductile cast iron specimens were austenitized at $900^{circ}C$ for 150 min and then austempered at $380^{circ}C$ for the various time periods from 15 min to 480 min. Mo added ADI had a higher volume fraction of retained austenite, and the volume fraction of retained austenite was determined by XRD analysis. As decreasing volume fraction of retained austenite, the elongation was also decreased as expected. But the UTS and yield strength were not decreased.