This paper intends to investigate the reality of the forced mobilization of Korean laborers to Hiroshima and Nagasaki and the Korean victims of the atomic bomb. Most of previous research on the Korean victims of atomic bomb have focused on revealing the situation by interviewing the survivors or on contemplating the significance of atomic bombs. Due to the absolute lack of related resources, the precise survey on the damage that the Korean victims suffered from has been considered almost impossible. During World War II, there was an influx of forcefully mobilized Koreans in Hiroshima and Nagasaki. Most previous studies failed to analyse them as victims of atomic bombings. In this paper, being aware that the study of the forced mobilization is an important process in order to study the victims of atomic bombs, I analysed the situation based on laborers’ lists and the documents about survivors. These are my conclusions of the research. First, by studying the conditions of forced mobilization, I could confirm the regions where the Korean victims were mobilized from and the extent of damage by atomic bombings. For example, there were many victims from Gyeonggi-do in Hiroshima while it has been generally known that they were moslty from Habcheon, Gyeongsangnam-do so far. On the other hand, in Nagasaki, there were about 10,000 workers mobilized from Korea, many of whom were from North Korea. Second, the aspects of the radiation damage appeared differently in Hiroshima and Nagasaki. The direct damage by atomic bombings was bigger in Hiroshima. In Nagasaki, relatively bigger was the indirect damage, caused by the remaining radioactive effects during rescue operations or restoration work.