This article analyses, the complex relationship between Tehran, Beijing and Washington on the Iranian nuclear issue. Indeed, China's policy towards Iran has often been described as ambiguous, in supporting Washington, on the one hand, while protecting Tehran, on the other hand. In this article, we argue that, in fact, Beijing policy vis-a-vis Tehran depends on the state of its relationships with Washington. Indeed, a closer analysis shows that China is using Iran as a bargaining chip with the United States on, among others, two key security issues, i.e., Taiwan and the oil supply. The guarantee of a secured oil supply from the Middle-East in addition to a comprehensive policy of the US with regard to Chinese security interests in Taiwan as well as the use of smart sanctions against Tehran, which would thus take into account, to a certain extent, Beijing economic interests in Iran, are, indeed, the guarantee of Beijing's support to the US policy towards Iran.