A series of fatigue crack propagation experiments were carried out in order to examine the effects of stress ratio R (=σ_min/σ_max) upon crack propagation rates, together with the closure and opening behaviours of fatigue cracks. Fatigue tests were conducted by using center notched specimens under cyclic axial loading in various stress ratios ranged from -5 to +0.8. Crack opening stress levels were determined by the unloading elastic compliance method. The variation of crack propagation rates under different stress ratios was well interpreted by the concept of effective stress intensity factor range ΔK _eff, defined as the product of ΔK and effective stress range ratio U . An expression of fatigue crack propagation rates, which is to be available under wide ranged stress ratios, was proposed on the basis of the present experiments and compared with those of other authors. The crack propagation behaviours near the threshold conditions are as well discussed.