In the wake of the recognition of the lack of relief measures and medical support for atomic bomb survivors (hibakusha) residing in South Korea, some Japanese dedicated themselves to assuring that Korean victims received subsidized medical treatment. This study assesses the significance of Japanese civil society-based medical support implemented by an anti-nuclear and relief organization, Kakkin Kaigi, and a Hiroshima-based doctor, Dr. Kawamura Toratarō. It also analyzes Japanese – South Korean citizen cooperation and the Japanese governmental relief program for hibakusha. In particular, it explains how Japanese grassroots movements succeeded in providing long-term medical support and eventually assuring that the Japanese government extend relief to long-neglected Korean victims.