Abstract: For the purpose of mass and energy change in decomposing course of Kandelia candel, the changes of dry matter, nitrogen, phosphorus and energy in decomposing course of Kandelia candel root in Jiulongjiang River estuary were studied with mesh bag method. The main results were as follows: the annual decomposition rates of the fine root （≤3 mm）and course root of K．candel were 96．9％ and 46．5％，170d and 392d for half-time of decomposition respectively, and both slower than its leaves for decompositian rate． Regression analyses showed that linear model was very well fitted with the data of dry mass loss against time． Nitrogen content and caloric value in the root of K．candel increased with root decomposing, increasing nitrogen 81．1％ and 43．8％ for fine root and course root after one year decomposing respectively, and decreased for phosphorus content, but energy, nitrogen and phosphorus amounts remaining in the roots rapidly declined with the rapid loss of the root matter.