Iran-China bilateral relations, established in 1971, have experienced quite substantial change in the post-1979 period, especially since the end of the Cold War. Both countries, despite fundamental differences in ideology and governance structure, and based on a number of areas of commonality, most prominently similar international outlook as developing states of the South, and based on mutual need in economic fields, most notably energy, and also in the military field, chose to expand their relations in various areas. The present article looks into the development of these bilateral relations since early 1980s and discusses two sets of factors that have impacted them; conducive factors and constraining factors. The article argues that while the conducive factors have contributed to the expansion and deepening of Tehran-Beijing relations during the period under review, China’s grand strategy towards becoming a world power and the requisite policy of rapprochement with the West, the U.S. in particular, have in fact intervened to constrain China’s relations with other states – among them, Iran. Simultaneously, perpetuation of a state of tension between Iran and the U.S. in the post-1979 period, and especially since 2003 over the nuclear issue, and hence, U.S. pressure of sorts on China, have also played a critical role in complicating Iran-China relations. China’s support since 2006 for the UN Security Council sanctions resolutions on Iran, despite Iran’s emphasis on the “Look to the East Policy” since 2005, has reflected the Chinese predicament and served to constrain the relations, even to some extent in the energy field. The article concludes that notwithstanding inevitable constraints in Iran-China relations due to the factors involved, both countries will continue to maintain their relations in the economic and energy fields and on international-multilateral issues of mutual interest.