Giga-cycle fatigue properties were investigated for an ultrafine-grained steel processed by warm tempforming. The fatigue properties of the tempformed (TF) steel were compared with conventional tempered martensite (QT) steel. Fatigue tests were carried out at frequencies of 20Hz and 20kHz, using servo-hydraulic and ultrasonic fatigue testing machines, respectively. Both theTF and the QT steels showed surface fracture in short life regions and fish-eye fracture in long life regions. The fish-eye fracture origins were oxide inclusions comprised of Si, Mg, Ca other than Al. Difference of fatigue strength was not notable between the TF and the QT steels, i.e. the fatigue strength of the TF steel was the same as that of the QT steel.