The purpose of the article is to characterize Mark Antonovichʼs activities at the Ukrainian Free Academy of Sciences (USA) as President of the UAN and to determine his contribution to the development of the Academy. Methods of research: historical-typological, historical-genetic, historical-system. Main results: An important contribution to the development and preservation of Ukrainian historical science can be considered the work of researchers in the scientific institutions of the diaspora in the twentieth century. The article analyzes the scientific and organizational work of Marko Dmytrovych Antonovych as an active member of the Ukrainian Free Academy of Sciences (UVAN). Marko Dmytrovych joined the scientific institution at the beginning of its foundation. The researcher took an active part in scientific conferences and fruitfully co-operated in the first group of History and Early History with auxiliary sciences, where Marko Antonovych served as secretary. After being elected President by the UVAN in the United States, he devoted himself entirely to the work of the organization. The scientist was in this position during 1992–1997. As the President of UVAN, M. Antonovych participated in the organization of scientific conferences speaking up with the reports. In addition, he was engaged in editing and preparing for the publication of scientific publications. During this period, under the auspices of UIA under the editorship or with the introductory word of M. Antonovych nine editions were published. On his initiative, the reorganization and modernization of the archive and library began. It was planned to inventory library and archival funds, the recruitment of a professional librarian and the purchase of a computer for the introduction of an electronic catalog (including the creation of e-mail). In addition, it was suggested to contact US and Canadian universities to collaborate on microfilming and preservation of some of the most valuable book and archive funds. It was during the presidency of Marko Dmytrovych that an agreement was signed on cooperation between the Ukrainian Free Academy of Sciences in the USA and the T. H. Shevchenko Institute of Literature of the National Academy of Sciences of Ukraine for ten years (1997-2007), the active cooperation of the Institute with UVAN in Canada, the Historical and Philological Section of NTSh and NTSh in Lviv, the Kyiv-Mohyla Academy, the Ukrainian Research Institute of Harvard University, the Harriman Institute and other academic institutions in America, Europe and Canada. UVAN occupied an important place in the organization of scientific life in the diaspora. Marko Antonovych, being a full member, and later also the President of the Academy, greatly contributed to the development of historical science. Thanks to his hard work, collections of archival materials and works by renowned scholars were published. His efforts to reorganize the archives and libraries also had a positive impact on the organization of the scientific activity of the UVAN, and, consequently, on the whole historical science. Practical significance: recommended for use in studying the activities of the Ukrainian diaspora, the work of scientific institutions abroad. Originality: A generalization of UAV activities in the United States was used during the period 1992–1997. Scientific novelty: documents from the UIT archive (Ukraine) and the UVAN archive (USA) were used for the first time. Article type: analitycal.