Fusion energy has been considered to contribute to reducing emission of carbon dioxide effectively. Understanding and evaluating the fracture toughness behavior of neutron-irradiated reduced-activation ferritic (RAF) steels are essential in the design and operation of fusion reactor. In order to produce an enough database of irradiation effects on materials, the reduction of the specimen volume is required to acquire an enough number of data points. In the ITER Broader Approach (BA) project, applicability of small specimen test techniques (SSTT) has been examined to evaluate irradiation-induced degradation of fracture toughness of F82H steel. The master curve method, which was provided by the American Society for Testing and Materials (ASTM), is specified as a standard test method for determination of reference temperature for ferritic steels in the transition range. Fracture toughness tests were carried out for F82H steel in order to evaluate the effects of specimen size on the shift of transition curve using the various sizes of specimens (1 CT, 1/2 CT and 1/4 CT). The master curve approach was made for evaluation of fracture toughness of F82H with subsized specimens with constraint loss by referring to the ASTM E1921. Small specimen tests can be applicable to evaluate the fracture toughness of F82H steel with no substantial effect of specimen size.