The anisotropy of fatigue crack propagation in hot rolled steel plate was studied for three orientations, viz., crack arrester, crack divider, and short transverse. The dependence of crack growth rate on stress intensity factor was shown to be sensitive to the microconstituents present and their orientation relative to the fracture plane and direction. Generally, this dependence increased as the material toughness decreased and when the mechanical fibering was parallel to the facture plane and direction. The macroscopic growth rates, were considered as the summation of several macroscopic mechanisms, including striation formation and inclusion-matrix fracture. The data show that striation spacing was independent of orientation and that the fracture of inclusions was primarily responsible for the observed crack growth anisotropy.