Combining field measurements with data from the literature, we quantified the C stock and potential C stocks in mangrove forests in China. China’s mangrove forests on average contain 355.25 82.19 Mg C ha1, store 6.90 0.57 Tg C in total, and have the potential to store from 9.8 to 33.0 Tg C, depending on the area occupied by mangroves and on the C density of the forest. These results indicate that mangrove forests play a critical role in C sequestration. Given that both the area and health of mangrove forests in China have been declining, maintaining and restoring mangrove forests in coastal areas of China is an urgent task.