Near-threshold fatigue crack growth characteristics was investigated on the Ni-Cr-Mo-V low alloy steel, which has the different microstructure obtained by tempering at various temperature. The specimens were austenized at 950℃ and then followed by tempering at 200℃, 530℃ and 600℃. Strain rate was obtained from strain gauge attached on the crack tip and crack opening point was observed through load-strain curve. Threshold stress intensity range(ΔK_(th)) was increased with increasing tempering tempuerature, but the effective threshold stress intensity rage(ΔK_(eff.th)) was not affected with the increasing temperature. Grain size increased with increasing tempering temperature.