Tropical forests are recognised for their high biodiversity and the roles they play in carbon (C) storage and their influence on climate. Tropical forests over limestone take up 40% of the total area of tropical Asia. Nevertheless, C cycling in tropical forests over limestone is poorly quantified. There is a need for robust measurement of ecosystem carbon storage in tropical forests over limestone. We assessed the ecosystem C stocks, not only aboveground biomass but also belowground biomass, forest floor and mineral soil (to 1 m depth) in a tropical forest over limestone on the northern edge of tropical Asia. Mean total ecosystem C stock was estimated as 214 ± 28 t C ha-1 (± SE). The contribution of plant biomass in storing C was substantial, accounting for 80% of the total ecosystem C storage. The mean C stock of tree layer was 155 ± 24 t C ha-1. Soil C stocks in tropical forests over limestone in this area (50 ± 10 t C ha-1) were
much lower than those in tropical forests from South-East Asia. Higher percentage of C stock in plant biomass while lower percentage in mineral soil indicated that C stocks of the tropical forests over limestone would be more vulnerable to vegetation destruction than other tropical forests on non-limestone substrate. This study gave an accurate estimation of C stocks of different components in tropical forests over limestone in Xishuangbanna and highlighted the important role they play in C sequestration.