This study surveys the history of Sino-Iranian relations from the early 20th century to the Islamic Republic, focused on the impact of Chinese politics on the Iranian left. At the beginning of the 20th century, traditional ties were replaced by new colonial networks of transportation and communication throughout Asia. News of the Iranian constitutional revolution quickly reached China and was debated by constitutionalists and colonialists in the pages of Shanghai-based newspapers. Competition and cooperation between Iran and the Republic of China emerged at the League of Nations in the 1920s and 1930s. Parallel to these ties, a robust, informal network emerged between the Tudeh Party, Iran’s pre-eminent Communist organization, and the Chinese Communist Party after 1949. The success of the Chinese Communist Revolution of 1949 helped inspire a more radical, internationalist approach to politics in Iran. Iranian youth increasingly saw themselves as part of a global community of oppressed nations. Many on the left, both secular and Islamic, studied Chinese texts and drew on Maoist theories to analyze Iran and international politics. China directly participated in and encouraged these developments, first by public support for the Tudeh Party, and later with clandestine support for an explicitly Maoist splinter group, the Revolutionary Organization of the Tudeh Party. This approach fills a gap in the existing scholarship of Sino-Iranian relations, which concentrates on elite interactions post-1979, by pushing back the timeline and foregrounding a set of unofficial connections typically relegated to margins of the historiography. It also emphasizes the global origins of the Iranian revolution and the international context in which it developed. The tangled relationship between the Chinese state, the Iranian state, and the Iranian opposition reveals a complex and sometimes controversial historical reality that is often glossed over by modern narratives of perpetual friendship and mutual co-operation. It rests on an analysis of primary sources in Mandarin and Persian, including Chinese media outlets, published interviews and travelogues from Iranians who went to China, Persian periodicals, and oral interviews.