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Effect of occasional mode II loading on subsequent mode I fatigue crackgrowth behavior was investigated by using a thin-walled tube made of 7075-T6511aluminum alloy. Careful observation of crack growth behavior revealed that theoccasional mode II loading has two contradictory effects for crack growth behavior.The first is a retardation effect that is associated with the plastic deformation nearcrack tip. However, this effect is negligibly small for the crack growth life as a whole.The second is an acceleration effect caused by mode II fatigue crack growth itself. Itwas found that under relatively high ΔK level, the mode II crack growth was about anorder magnitude faster than mode I crack growth. Therefore, to properly evaluate theeffect of occasional shear loading in the 7075 alloy, the mode II crack growth should betaken into account.