Carbon stock and the distribution of an 8-year-old Acacia cincinnata plantation in Nanning, Guangxi, China, were investigated based on field sampling data. The results showed that carbon content in different organs of A. cincinnata ranged from 465.8 to 508.2 g·kg^-1, and it was distributed in a descending order as follows: stem＞leaf＞branch＞root＞bark. Carbon content in the soil (0-80 cm) was 8.44 g·kg^-1 which declined with soil depth. The carbon stock in A. cincinnata plantation ecosystems was 126.07 t·hm^-2, which distributed among the tree layer with a stock of 28.76 t·hm^-2, shrub layer 5.35 t·hm^-2, herbaceous layer 1.25 t·hm^-2, litters 1.69 t·hm^-2, and the soil layer (0-80 cm) 89.02 t·hm^-2. Annual net productivity of A. cincinnata plantation was 10.15 t·hm^-2·a^-1, and annual carbon storage was up to 5.64 t·hm^-2·a^-1.