The physical and chemical characteristics of Ductile Cast Iron(DCI) have been well known because of many studies about DCI. So it has a wide application in the field of heavy and automobile industry because DCI has a good combination of excellent castability and good mechanical properties. But its usage has been often restricted to use in parts such as exhaust manifold required high heat resistance in automobile industry. So, in this study, in order to achieve high heat resistance in DCI, DCI with addition of high Si and Mo alloy elements have been researched on mechanical properties, including heat resistances systematically. With the increase of Mo and Si content, the size and number of graphite in matrix of DCI increased and the pearlite in DCI matrix is transferred to ferrite because of Si strong former of ferrite, otherwhile carbide in matrix increased because of Mo carbide former. In the test of oxidation property, Si and Mo played an important role to retard oxidation of DCI. By the: addition of Si and Mo, the Charpy impact energy was decreased, whereas the total hardness was increased. (Received February 20, 1998)