Tests were carried out to measure temperature rise of specimens together with damping constant due to the internal friction of materials, during the fatigue test. Temperature rise is a function of the magnitude of cyclic stresses, and a relationship between temperature rise and life of the specimen is found. Damping constant c is influenced by temperature of specimens, and has no relation to the magnitude and the cycle number of stresses after considerable repetitions. When plotted c under fatigue tests and damping constant measured by torsion pendulum against temperature, the curves thus obtained have shapes similar to each other, having the same temperature for extreme point. And the fatigue strength vs. temperature has an inverse shape of the former. Further, scatters of fatigue lives are found to be influenced by the differences of damping constant, that is, temperature rise of specimens.