A toughness-improved type of F82H steel called F82H mod3 has been developed, and the material properties and irradiation behavior have been examined. The significant modification of the chemical composition is the reduction of Ti (<10 ppm) and N (<20 ppm) as impurities and the increase of Ta (0.1%) as an alloying element. The ductile-to-brittle transition temperature (DBTT) is improved to -90°C from -45°C for F82H IEA without change in strength. However, the creep rupture time of F82H mod3 was 1/10 of F82H IEA. Another feature of the F82H mod3 is the stability of the material properties. Higher temperature normalization (1080°C) degrades the DBTT only to -80°C due to grain coarsening without large change in strength. It is quite important for large-scale production of the material in high quality. Preliminary neutron irradiation experiments up to 17 dpa showed better irradiation resistance to changes in fracture toughness than F82H IEA.