Abstract: The total respiration rate of artificial Acacia mangium forest (tree layer) was estimated in low subtropical hill region of Guangdong province. The respiration rate was determined by infra-red CO2 gas analyzer with a large number of detached samples of leaves and woody organs taken from trees of various sizes. Using pipe model theory, the formulas of diameter frequency distribution and the relation of the respiration to its diameter for woody organs were established. Accordingly the formulas for total respiration rate of woody organs and leaves were then given. Results showed that the respiration rate of woody organs was negatively correlated with diameter and the total respiration rate was positively correlated with DBH and height (D2H). The yearly total respiration rate of Acacia mangium forest was calculated to be 47.51 t CO2·hm-2, trunk, branch, leaf and root accounted for 23.1%, 13.9%, 48.7 % and 14.4 % to the total respiration rate, respectively.