Abstract: This study examines how Cultural Revolution factionalism transformed ethnic relations in a Sino-Korean borderland, based on archival, memoir, and leaflet literature of the decade in addition to recent field interviews. At the start of the Cultural Revolution, Mao Zedong’s nephew Mao Yuanxin went to the Yanbian Korean Autonomous Prefecture (延边朝鲜族自治州) with orders from Jiang Qing and Chen Boda to build a power base. While seizing power from local cadres, Mao Yuanxin forcibly suppressed some core elements of the Korean ethnic identity through a campaign of escalating factional violence. Its aftermaths affected both local Han and Korean people, but disproportionate losses went to the Koreans, whose political status, institutional power, and psychological perception of their prospects in the Chinese political system suffered profound damages. The Cultural Revolution in Yanbian caused a major rupture in the mutually supportive relationship between the Chinese Communist Party and the Koreans in Manchuria since their interests converged during the Anti-Japanese War.