The effects of alloying elements vanadium and molybdenum on hardness and the linear thermal expansion coefficient of the Invar-type austenitic cast irons were investigated. A combined addition of vanadium and molybdenum was found to be the most effective for the improvement of hardness without causing an increase in the thermal expansion coefficient. Without heat treatment, the hardness value increased up to 180 HB, and the thermal expansion coefficient was kept at a relatively low value of 4.6 x 10(-6) K-1 with a combined addition of 4.6 wt % V and 3.8 wt % Mo. The effects on the damping capacity of graphite morphology, the magnetic domain, and the combined addition of vanadium and molybdenum were also investigated. The good damping capacity of Invar-type cast irons was mainly the result of stress absorption in graphite. As the amounts of vanadium and molybdenum increased, the damping capacity decreased. This is caused by an increase in the amount of carbides.