The article undertakes a comparative analysis of strategies and forms of implementation of the defense diplomacy of Japan, China, and Russia in Southeast Asia. All the three above-mentioned countries seriously accelerated their defense ties with the states of the region in the 2010s both at the bilateral track and within the multilateral frameworks. The article focuses on Japan, China, and Russia due to the specifics of their relations with the region. All three countries have historical limitations in developing defense diplomacy in Southeast Asia. However, as this article argues, throughout the past decade, all the three have been actively emphasizing defense diplomacy as one of the pillars of their advancement in the region. There is a number of publications, in Russia and abroad, which study either bilateral forms of defense diplomacy or the activities of such ASEAN-centered regional institutions as the ASEAN Regional Forum, ADMM+, the ASEAN Expanded Maritime Forum, or externally generated frameworks like the Shangri-La Dialogue. However, up to nowadays, none of these publications undertook a comparative analysis of defense diplomacy strategies and tactics of Japan, China, and Russia. This article aims to bridge this analytical gap. Methodologically the article undertakes the comparative analysis of defense diplomacy of the three countries in question. The main parameters for comparison were the doctrinal frameworks of defense diplomacy (analysis of national security documents), case studies of the Southeast Asian states most important for the advancement of Japan, China, and Russia’s defense diplomacy and the instruments of defense diplomacy development at the bilateral (intergovernmental frameworks, military-technical cooperation, joint exercises, port calls, etc.) and multilateral levels (within ASEAN-centered institutions).