This article outlines the spread of the Bahá’í religion—known in Chinese as Datong jiao 大同教)— as a form of religious cosmopolitanism in Republican China (1912–1949). Originating in Iran, its spread to China can be traced to links with the Ottoman empire, British Palestine, the United States, and Japan. By tracking the individuals, connections, and events through which knowledge of the Bahá’í movement spread in China, our study reveals an overlapping nexus of networks—intellectual reformers, liberal Christians, Esperantists, Confucian modernizers, redemptive society activists, and socialists—that shared cosmopolitan ideals. The Bahá’í connections thus serve as a thread that reveals the influence of a unique ‘cosmopolitan moment’ in Republican China, hitherto largely ignored in the scholarly literature on this period, which has focused primarily on the growth of modern Chinese nationalism. Leading nationalist figures endorsed these movements at a specific juncture of Asian colonial modernity, showing that nationalism and cosmopolitanism were seen as expressions of the same ideal of a world community. We argue that the sociology of cosmopolitanism should attend to non-secular and non-state movements that advocated utopian visions of cosmopolitanism, map the circulations that form the nexus of such groups, and identify the contextual dynamics that produce ‘cosmopolitan moments’ at specific historical junctures and locations.