Abstract. A fatigue properties evaluation method by small specimen test technology has been developed. A miniaturized hourglass-shaped fatigue specimen (dimensions: 25.4L×4.96W×1.52T mm3), which was designed for usage in the IFMIF (International Fusion Materials Irradiation Facility), enables to evaluate the fatigue properties as well as conventional large specimen. Furthermore, focused ion beam micro-sampling method has enabled microstructural analysis on fracture process precisely. In this work, the effects of radiation damage and transmutation helium on the fatigue properties of F82H were investigated. Low temperature neutron irradiation and helium-ion-implantation caused 100 MPa of radiation hardening and the hardening degraded the fatigue lifetime of F82H at ambient temperature. Microstructural analysis revealed that this degradation of fatigue lifetime was caused by local brittle fractures occurred at early stage of fatigue tests. In case of helium-ion-implanted samples, the deformed microstructure seemed to be similar to that of neutron irradiated one. These results imply that 100 appm of implanted helium did not degrade the fatigue fracture properties drastically.