This article seeks to fill a gap in the literature by sketching a narrative of Republic of China–Iran relations between 1920 and 1949. It analyzes the factors behind Sino-Iranian cooperation and competition in the tea and silk trades and at the League of Nations. Unofficial commercial interests, including Iranian merchants in Shanghai, played a larger role than previously thought in driving the establishment of the Sino-Persian Treaty of 1920. After ratifying the treaty in 1922, the Republic of China established an Iranian consulate in Shanghai in 1934. Diplomacy between the two nations, and the public ceremonies performed by foreign diplomats in Shanghai, were part of a pattern of performative nationalist diplomacy undertaken by both the Chinese and Iranian states.