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Ductile iron discovery in 1948 gave a new lease on life to the cast ironfamily. In fact these cast irons are characterised both by a high castability and by hightoughness values, combining cast irons and steel good properties. Ductile cast ironsare also characterised by high fatigue crack propagation resistance, although thisproperty is still not widely investigated. In the present work we considered threedifferent ferritic-perlitic ductile cast irons, characterised by different ferrite/perlitevolume fractions. Their fatigue crack propagation resistance was investigated by meansof fatigue crack propagation tests according to ASTM E647 standard, considering threedifferent stress ratios (R = Kmin/Kmax = 0.1; 0.5; 0.75). Crack surfaces were extensivelyanalysed by means of a scanning electron microscope. Crack paths were investigated bymeans of a crack path profile analysis performed by means of an optical microscope.In order to analyse ferrite/perlite volume fractions and graphite spheroids influence,da/dN-∆K fatigue crack propagation results were compared with profile and fracturesurface analysis.