In order to investigate the recovery behavior of defect clusters in reactor pressure vessel (RPV) steels, three kinds of Fe-Cu binary alloys and one kind of Fe-Cu-C ternary one, which were irradiated with neutrons at 573 K to about 0.003 dpa, were annealed at 723 K for 7 hours or irradiated at 723 K again to 0.0003 dpa. Microvoids, interstitial clusters and Cu precipitates were formed after irradiation at 573 K in all alloys. In Fe-Cu alloys, microvoids and interstitial clusters disappeared, and Cu precipitates were formed either by annealing or irradiation at 723 K. The dissolution of interstitial clusters and the formation of Cu precipitates were more prominent in irradiation than in annealing at 723 K. In Fe-Cu-C alloy, the decrease of vacancy clusters and formation of Cu precipitates had the same tendency as in Fe-Cu alloys except annealing at 723 K, where Cu precipitates were not formed.