To compare Brinell Hardness of irradiated rolled copper plate with unirradiated one, the copper plate is annealed for two hours at 150℃, 200℃, 350℃, 450℃, 600℃, and 800℃ respectively and irradiated in Reactor with total thermal neutron flux 7×10^(17) nvt and fast neutron flux 2.3×10^(17) nvt. Copper plate which was annealed above recrystallization temperature increase its hardness when irradiated with neutron. The increasing hardness ratio of irradiated copper plate which was annealed above 450℃ is, 6%, while annealed under recrystallization temperature shows softening. Such characters are explained by formation of defects and elimination of stress field by forming thermal spike in crystal structure. And by annealing for two hours above 200℃, the defects which cause radiation hardening are fully recovered.