Abstract To examine the effect of oxide layer thickness on fatigue behavior, rotating bending fatigue tests were performed on the aluminum alloy A2014-T6 with oxide layers of 3 different thicknesses in laboratory air and 3 % sodium chloride (NaCl) solution over a wide cycle-life region (104–109 cycles). Tests were also conducted on untreated specimens for comparison. Based on the results of fatigue tests in laboratory air, deterioration of the fatigue strength was observed for anodized specimens having an oxide layer in comparison with untreated specimens. The fatigue strength of anodized specimens decreased with increasing oxide layer thickness. On the other hand, fatigue test results in 3 % NaCl solution showed that anodizing improved fatigue life, which increased with increasing oxide layer thickness. In addition, the thickness of the oxide layer was found to be important from the viewpoint of fracture mechanics.