Abstract: Fatigue lives for the smooth and notched specimens of 8090 Al-Li alloy jn the different ageing conditions have been studied. For the smooth samples of 8090 alloy the artificial ageing results in an increase in fatigue life in comparison with natural ageing. On the contrary, the notched specimens of 8090 alloy in the naturally aged condition show higher fatigue life than in the peak-aged. The exposure to either the peak-aged or naturally aged leads to superior fatigue properties of Al-Li alloy to the traditional high strength aluminum alloys of 7075 and 2024, especially in the latter aged condition. In all ageing conditions, i,e. naturally, under-, peak- and over-aged, the peak-aged 8090 alloy displays the highest fatigue life and the over-aged material has a minimum value at the same stress amplitude. The difference in fatigue life is mainly attributable to the size and distribution of strengthening precipitates as well as the wide of precipitate free zones (PFZ's) along grain boundaries.