The fatigue properties of friction stir (FS) and TIG welded Al 6N01-T5 alloys were compared in the present study. The low cycle fatigue (LCF) test was performed under total strain amplitudes in the range of ± 0.6 ~ ± 1.5% and with a strain rate of 3 x 10-3/s. During low cycle fatigue, the base metal showed little cyclic hardening or softening, whereas both the FS and TIG welded zones showed a large amount of cyclic hardening until fracture, although the fatigue life of the TIG welded zone was much shorter than that of the FS welded zone. The fatigue crack growth rate (FCGR) was retarded in the heat affected zone (HAZ) on the advancing side of the FS welded zone, due to the compressive residual stress in this region. The differences in the fatigue properties in these two welded zones were discussed in terms of the microstructural changes during fatigue.