Abstract:The nutrient dynamics during the decomposition of coarse woody debris （CWD） with different diameters from Castanopsis chinensis in Dinghushan monsoon evergreen broadleaved forest, Guangdong Province, was examined by sampling debris that were at various decaying stages. Changes in debris density were measured in debris with diameters of 5-10 cm （grade 1）, 10-20 cm （grade 2） and 20-30 cm （grade 3） to study the composition rates, nutrient dynamics, and substrate quality during decay. Up to decay stage HI, CWD grades 1, 2, and 3 lost its weight and carbon by 36%, 48% and 43%, and 33%, 47% and 19%, respectively. The concentrations of N, P, Mg, Ca and Na increased while C and K decreased. The increase in element content was likely due to lower leaching rate campared to the loss of CWD mass. N accumulation in CWD might be caused by nitrogen fixing bacteria and fungi. The change in ratio of N to P showed a good decomposition indicator in CWD. The release of carbon and other main nutrients was slow, thus CWD exhibited an important long-term carbon sink in the forest.