The effects of structural constituent on the thermal fatigue properties of Ni grain roll material applicated to finishing work roll for hot strip mill has been investigated. Graphite area ratio varies with the depth from roll surface in the range of 4-7.5%. The morphology of crystallized graphite showed particle shape at surface of roll and changed to coarse flake with increasing depth from roll surface. Thermal fatigue resistance was impaired with increasing graphite area ratio, due rather to the notch effect of graphite resulting in the strength of matrix being reduced, than to thermal stress developed showing little differences with graphite area ratio and morphology in the case of severe heating and cooling conditions.