Fracture toughness and fatigue crack growth data of four nodular cast irons with different pearlite fractions are studied. The influence of temperature on fracture toughness is also investigated. Fracture surfaces are observed using a scanning electron microscope to correlate fracture toughness with the fracture surface and to understand the mechanism of crack growth at different stress intensity factor ranges. It is shown that the upper shelf fracture toughness increases with pearlite fraction. The existence of nodular void regions on the fracture surface plays an important role in fracture toughness. The fatigue crack growth rate is less sensible to stress intensity factor range when pearlite fraction increases.