ABSTRACT Peace efforts to resolve the Indonesia-Malaysia conflict (1963–1966) became an important agenda in Japan’s Southeast Asia policy under Prime Minister (PM) Eisaku Satō. After a cautious start, the Satō government sought to create conditions for the Indonesians and Malaysians to end their armed confrontation (confrontation), which had become a source of destabilisation in Southeast Asia. Japan’s peace efforts began under PM Hayato Ikeda (1960–1964), marking the first time after World War II that Tokyo became involved in attempts to mediate a conflict. These endeavours were carried out in a region where mixed feelings lingered towards Japan for its wartime occupation. This paper investigates the factors that shaped the Satō administration’s engagement in efforts to resolve the confrontation and sheds light on how Japan’s relations with the United States (US) influenced its peace-making role – an aspect on which little has been written in previous studies. The findings indicate that considerations related to Japanese relations with the US were an important driver, although not the only one, of the Satō administration’s diplomatic initiatives to resolve the Indonesia-Malaysia armed confrontation. Furthermore, Japan’s peace efforts contributed to the US policy in Asia.