The effect of specimen size and specimen shape on the fatigue life of reduced activation ferritic steel, F82H IEA-heat, was investigated to develop the fatigue life evaluation method using small specimen for testing 14 MeV neutron irradiated materials. The fatigue test was carried out at room temperature in air using three kinds of round-bar specimen (the minimum diameter of the cross section: 1, 4, and 7 mm) and one hourglass specimen (the minimum diameter of the cross section: 1.25 mm). The effect of specimen size on the fatigue life was almost negligible for the round-bar specimens. The shorter fatigue life at relatively low strain range and slight longer fatigue life at relatively high strain range for the hourglass specimen than the standard specimen were observed.