The study estimated the carbon sequestration potential of 25 year old Tall x Tall coconut (Cocos nucifera L. variety typica) plantations under S 2 (highly suitable for coconut) and S 4 (moderately suitable for coconut) soils in wet (WL 3 , high moisture availability), intermediate (IL 1a , moderate moisture availability) and dry (DL 3 , low moisture availability) agro-climatic conditions during May to September 2009. Variation in total carbon stock (plant and soil), total carbon input (measured as Gross Primary Production of coconut, GPP), total carbon output (measured as plant and soil respiration) and net carbon balance of ecosystems were assessed. Eight coconut palms and sample plots per site were used for estimations (two factor factorial with eight replicates). There is a significant agro-ecological region (AER) x land suitability class (LSC) effect on all the components of the carbon balance in a coconut plantation. The total ecosystem carbon stock (B tot-eco ) reduces along a decreasing moisture gradient from WL 3 to DL 3 and decreasing soil fertility gradient from S 2 to S 4 . The GPP and R tot-eco do not show a reduction along a decreasing moisture gradient from WL 3 to DL 3 on S 2 , whilst it shows a reduction from WL 3 to DL 3 on S 4 . The net C balance reduces from WL 3 to DL 3 on S 4 , whilst it does not reduce from WL 3 to DL 3 on S 2 . C stock of the ecosystem varied between 32 and 72 Mg C ha -1 whilst the net carbon balance varied between 0.4 and 1.9 Mg C ha -1 month -1 under different growth conditions. Of the measured components, GPP and maintenance respiration of coconut palms and soil respiration had greater contributions to the overall C balance of the system. This is the first report on carbon sequestration potential in coconut plantations of Sri Lanka.