In China, a large private sector has evolved alongside a still sizeable state-owned sector that is subject to government control. Several studies have found that in this mixed economy, the private sector is economically more efficient than the state-owned sector. In this paper, we investigate whether private firms are also more carbon efficient than state-owned firms. Using a macroeconomic panel data model with provincial data from 1992 to 2010, we confirm that private firms emit less carbon dioxide than state-owned firms. Our results imply that future reforms, such as ongoing privatization, introduced to increase the economic efficiency of state-owned companies will also mitigate emissions growth. The policy lesson, not only for China but for developing countries maintaining a large state-owned sector, is that economic efficiency and energy efficiency are conjoined mutual benefits.