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Dynamic testing methods, especially the Charpy V-notch testing at different temperatures, are commonly used to determine the impact response of metallic materials. However, in nodular cast iron this transition trend is characterized by scatter, which makes it difficult to precisely identify the influence of microstructural features on material response. In this paper the vertical surface roughness parameter RV obtained from fracture profiles is considered on the hypothesis that the surface topography is a sensitive indicator of the energy absorbed by plastic deformation and of the microstructure. Nodular cast irons having a range of microstructures were impact tested and the surface roughness determined. Transition trends of impact toughness and of RV are discussed.