Mantle CO₂ is widely distributed throughout the basins of the world. Risks are associated with its accumulation that have recently attracted attention in the oil and gas exploration industry. It is, therefore, necessary to determine the mantle CO₂ distribution in a target region, which involves determining the locations of the CO₂ sources, migration pathways, and areas of accumulation. In this paper, the potential accumulation of mantle CO₂ across the East China Sea (ECS) basins is analyzed using the source and migration pathways. The results show that areas of Moho uplift (including paleouplift) correspond to areas of CO₂ sources (including paleosources). Steep extensional faults, which penetrate the lower crust and upper mantle, and diapiric structures likely provide for mantle CO₂ migration. These results can be used to develop general principles for locating mantle CO₂ sources and pathways in rifted basins. Within the ECS basins, the Lishui, Jiaojiang, and Diaobei sags are considered high-risk areas for CO₂ accumulation. The Xihu and Fuzhou sags are medium-risk areas, and the remaining sags are low-risk areas. The areas along the Lingfeng, Yandang, Fuzhou, and Xihu-Jilong faults are potential CO₂ accumulation areas. This study indicates that the accumulation of mantle CO₂ in the ECS basins can be predicted from the Moho depth distribution, fault systems, and traps across the region.