PurposeThis paper aims to deepen understanding of the interrelated questions: how Japanese antidumping policies have been formulated and transformed; what the reasons are for such caution in adopting antidumping measures; and what patterns can be observed of recent changes in antidumping policy and legal systems.Design/methodology/approachTo explain the changes in antidumping policy and rules in Japan, this paper examines not only political competition among bureaucratic organizations but also policy learning by bureaucratic organizations and their effects on change in policy preferences and advancements in the legal system.FindingsThe effects of bureaucratic politics and policy learning not only complexly interact but also are highly complicated to initiate policy changes in accordance with the maturity of antidumping legal system. In this case study, the policy learning has led the rival bureaucrats to a consensus to change antidumping policy and legal system, but the agreement could be a temporal truce that may easily collapse by political contingencies.Originality/valueAlong with the influences of large‐scale economic and political dynamisms, this paper focuses on two aspects of the policy subsystem to explain those changes: one is political competition among bureaucratic organizations claiming jurisdiction of antidumping policy; the other is the effect of policy learning among bureaucratic organizations on changes in policy preferences and on advancements in antidumping rules.