Low-temperature, low-cycle fatigue strength of aluminum alloy welded joints were investigated, carring out deflection controlled repeated bending fatigue tests at room temperature and at -196°C on the following four materials : 5083-O plate, 5083/5183 butt weldments with and without reinforcement, and Tee-fillet weldments made by MIG welding process. The results showed the fatigue properties at -196°C to be superior to those at room tem..' perature, except for the butt weldment with reinforcement machined off in the fatigue life range less than 100 cycles. The fatigue strength ratio at both temperatures increased with increasing fatigue life up to about the ultimate tensile strength ratio at both temperatures. The strain-basis fatigue strength reduction factor due to the reinforcement of the weld K_f ., as difined by the ratio of the fatigue strength of the weldment to that of the 'plate, was found to be essentially the same at both temperatures and to become greater than or equal to the elastic stress concentration factor at the weld toe. The above mentioned factor K_f ., was reasonably evaluated by Stowell's equation. From these observations it is concluded that the application of the fatigue strength at'room temperature as an allowable stress in the fatigue design of LNG tanks will be on the conservative side.