For many years, Nagasaki University, particularly the Atomic Bomb Disease Institute, has been engaged in research regarding the late health effects of radiation exposure in Nagasaki atomic bomb survivors. Since 1991, we have participated in several Chernobyl projects including the Chernobyl Sasakawa Medical Cooperation Project which demonstrated a marked increase in the incidence of childhood thyroid cancer around Chernobyl, especially in the Gomel region, Belarus. Furthermore, we have performed both fieldwork and research to clarify the late effects of radiation exposure around Semipalatinsk Nuclear Testing Site and participated in bilateral official medical assistance projects between Japan and Kazakhstan to strengthen the medical infrastructure in this area. Through these humanitarian and scientific projects, we have been collaborating closely with our counterparts in the former USSR for the past 15 years. Here, we present a brief review of our past activities and future directions of international cooperative radiation research from Nagasaki to Chernobyl and Semipalatinsk.