The aim of this study is to establish a standard for evaluating factors affecting awareness of nurses in initial response to nuclear/radiation disasters and to examine its reliability and validity. Based on the “planned behavior theory” proposed by Ajzen in 1985, related items were extracted from prior studies, and a draft of the standard was created based on meetings of experts in this field as well as pilot studies. An anonymity questionnaire was prepared for nurses who belonged to the disaster base or nuclear disaster base hospitals or cooperation institutions for nuclear disaster medicine, who had nursing experiences related to radiation disasters, or who might be called upon in case of nuclear/radiation disasters (1,480 nurses from 740 facilities). From results obtained by item or factor analysis based on the questionnaire, “A standard to assess factors affecting awareness of nurses in initial response to nuclear/radiation disasters” was established consisting of 5 factors (practical knowledge, role expectation from others, intention for specialization, collaboration system, uneasiness about radiation exposure) with 23 items. Reliability and validity were confirmed by internal consistency, contents validity, construct validity, and examination of discrimination validity. This standard will enable the establishment of a training system for the initial response to nuclear/radiation disasters and evaluation of the system.