Fatigue crack growth behavior has been investigated for micro-sized Ni-P amorphous alloy specimens. Cantilever beam type specimens (10 μm by 12 μm by 50 μm) with notches were prepared from Ni-P amorphous thin film by focused ion beam machining. Fatigue crack growth tests were carried out in air at room temperature using a newly developed mechanical testing machine that can apply cyclic loading to micro-sized specimens. Striations were observed clearly on the fatigue surface, and fatigue crack growth resistance curves as a function of stress intensity range (ΔK) were obtained from careful measurements of the striation spacings. The fatigue crack growth rates at stress ratios of 0.3 and 0.5 were greater than that at 0.1 under a given value of ΔK. This suggests crack closure may occur even in such micro-sized specimens and may affect the fatigue crack growth behavior.