This article examines the role of scientific experts in the post-war Japanese antinuclear power movement. It argues that experts and their movements have influenced the development of nuclear power in Japan, albeit in an indirect, constrained and sporadic way. Experts like the nuclear chemist Takagi Jinzabur? stimulated an upsurge of antinuclear protest and public opinion, especially after the Chernobyl accident in 1986, which made power plant siting more difficult, contributed to longer construction lead times, and forced state and nuclear industry officials to devote considerable resources to atomic energy public relations (PR) campaigns and compensation for nuclearised communities. The antinuclear advocacy and activism of scientific experts arguably helped to slow down nuclear power development, resulting in a less nuclearised Japan than imagined by its advocates. Antinuclear experts and their movements, however, never became players in mainstream nuclear policymaking and had to be content with pressure tactics from the political peripheries. After the Fukushima Daiichi Nuclear Power Plant disaster of March 2011 some observers pointed to this lack of direct political influence as evidence of the failure of the antinuclear movement. Rather than outright failure, however, this article presents a more ambivalent history marked by both achievements and shortcomings.