Abstract: The research object is the history of the People’s Commissariat for Internal Affairs. The research subject is the Organization of Ukrainian Nationalists and its battle group - the Ukrainian Insurgent Army. The article studies the experience of the Internal Affairs bodies’ struggle against the Organization of Ukrainian Nationalists, the Ukrainian Insurgent Army, which became a symbol of the national-separatist movement in postwar regions of Western Ukraine. The purpose of the research was to analyze the practice of the Internal Affairs bodies’ struggle against the nationalist armed groups of the Ukrainian Insurgent Army in 1944 - 1955. The research task was to consider various measures aimed at the extermination of nationalist armed groups in postwar Western Ukraine. The research methodology is based on analysis and synthesis, and the historical-legal analysis of events. The scientific novelty of the research consists in the need for a comprehensive study of the experience of struggle against armed national-separatist groups in the context of complicated Russia-Ukraine relations after the 2014 armed coup in Kyiv which resulted in radicals coming to power, who use the ideas of the OUN-UIA and the postwar experience of struggle against official authorities. The topicality of the research consists in the fact that the experience of military and ideological struggle against the Internal Affairs bodies of the Ukrainian Soviet Republic has been actively used by the modern Security Service of Ukraine. Territorial claims to Russia’s south-western areas are expanding, which are believed to belong to the Ukrainian Republic by Ukrainian radicals. The author’s contribution to the research of the topic is the definition of the strategy and tactics of internal affairs and security bodies of the Ukrainian Soviet Republic aimed at the elimination of nationalist armed groups. The author defines the reasons which impeded the work of internal affairs bodies during the suppression of armed separatism.