This paper describes the effects of overload on the ΔKth of aluminum alloy. Tensile or compressive overload was applied to compact tension specimen, subsequently fatigue tests were carried out at stress ratio R=0. 1. The main conclusions are as follows; (1) The value of ΔKth increased with increasing of the tensile overload. (2) The effect of compressive overload on ΔKth was small. (3) The effect of overload on ΔKth depends on neither the yield strength nor Young's modulus.