It is very important to clarify the question whether fatigue crack propagation will be affected by mechanical propaties or other propaties of materials. In the present paper the authors studied in relation of yield strength and stacking fault energy to rate of fatigue crack propagation. αbrass were chosen for the investigation because they provided sufficient range in both quantities of interest that either could be varied independently of the other. Fatigue tests were carried out under full bending moment of flat specimens with V-shape notch. Chosen stress levels were 0.6 σy and 0.8 σy in which σy is yield strength, rate of fatigue crack propagation was evaluated from the second stage of the curve of fatigue crack propagation. The dependence of the rate on stacking fault energy γ was found to be dl/ dN=G・γ(n). But dl/dN did not systematically to change in yield strength. Thus, γ is concluded to be the controlling variable.