Two kinds of tests were carried out using aluminum alloy 5083-O plate and butt weldments at several temperatures : One is the tensile test and the other is the fatigue test. Tensile tests were conducted on solid cylinder specimens of 10 mm in diameter at several temperatures ranging from 10°C to-196°C. The tests revealed that there was the following relationship between ultimate strength ( S_u ) and absolute temperature ( T ); log ( S_u ) = A + B/T where A is a constant dependent on specimen type and B is a material constant. On the other hand, the fatigue tests were carried out at 10°C and-170°C on the 35 mm thick test specimens : base metal, butt welded joint without reinforcement and butt welded joint with reinforcement. The results showed that the fatigue strength in terms of nominal stress range (? S ) could be expressed by the following formula ; log (? S ) =log ( C )- k log ( N_f ) where k is a constant, C is a constant dependent on specimen type and temperature, and N_f s the number of cycles to failure. Through these experiments, it has been found that there is a linear relationship between C and ultimate strength ( S_u ). And the following empirical formula for normarized stress range (? S/S_u ) was obtained ; log (? S/S_u ) =0.612-0.16 log ( N_f ) where ? S is the actual stress range in consideration of strain concentration due to the weld toe. This means that fatigue strength at any temperature can easily be evaluated by conducting tensile test for specimens at a temperature under consideration together with relatively easy fatigue test at room temperature.