The balance of C is one of the most important balances in nature, since it determines the flow of organic matter, governs that of other bioelements (N, P, S, etc.), and controls the content of CO2 in the atmosphere. The objective of this work was to quantify the C sequestration in a Sweet chestnut forest located in the «Sierra de Gata» Mountains (Central-Western Spain). This chestnut coppice is located in the south edge of the «Sierra de Gata» mountains (province of Cáceres, central-western Spain). Climatic characteristics are mean temperature 15 ºC and mean annual-rainfall 1,158 mm yr-1, i. e., sub-humid Mediterranean. The soils are an association of haplic Umbrisols and Leptosols. This coppice of Castanea sativa is 25 years old, i. e., the usual rotation time. The accumulations of C in the tree biomass was 58 Mg C ha-1 yr-1, the calculated litter decomposition-constants 0.39 yr-1, and the aboveground annual-production 5.25 Mg C ha-1 yr-1. The accumulation of C in the Ah horizons was 143 Mg C ha-1. On calculating a global balance, inputs of C into this forest ecosystem are always greater than the C outputs, the excess being 4.7 Mg C ha-1 yr-1.