Abstract: The effect of fretting on fatigue lifetime of LY12CZ aluminium alloy is experimentally investigated. The results show that for the same cyclic bulk stress the fretting fatigue lifetime is low and up to 45% of the normal fatigue lifetime. For the structure suffered by fretting, the time for the initiation of fatigue crack is very short and is only 15% to 20 % of the whole fatigue lifetime. The propagation lifetime of fretting fatigue crack decreases as the normal load and the ratio Q/fP increase, but increase as the pad curvature radius increases. While the ratio N_p/N_t increases as normal load and the ratio Q/fP increase, and decreases as the pad curvature radius increases. Of these parameters, the ratio Q/fP hadve the most pronouced effect on N_p/N_t, followed by the normal load P. The pad curvature radius has the least effect on N_p/N_t.