Abstract: 1561 aluminum alloy butt welded joints were prepared by metal arc gas welding.At room temperature, the low cycle fatigue experiments were performed with the strain ratio of 0.1 and the cyclic frequency of 3 Hz.The effects of the strain amplitude on the fatigue life were discussed.The fatigue fracture features were analyzed.The results show that the low cycle fatigue life of the welded joints decreases with the increase of strain amplitude.The fatigue fracture is divided to three regions of crack initiation zone, crack stable growth zone and transient fracture zone. The fatigue life depends on the area of crack stable growth zone, the blowholes close to the surface and intermetallic compounds are the main crack nucleation sources.Therefore, the control of the formation of blowholes and intermetallic compounds in the welded joints is the key to improve the fatigue life.