The fatigue crack propagation behavior of several TRIP (Transformation Induced Plasticity) steels was investigated by tensile and fatigue tests and by metallographic and fractographic techniques. The nominal composition of the steels was Fe-0. 25C-9CR-8Ni-3Mn-3Si-4Mo. The effect of thermomechanical processing was included in the study. A beneficial effect of strain induced martensite transformation was found. TRIP steels showed better fatigue crack propagation properties than a number of alloy steels of similar strength levels and compared favorably with maraging steels in the low stress intensity range.