Aboveground nighttime respiration of mangrove Kandelia obovata trees in the northernmost limit of their distribution was measured monthly throughout a year to investigate size-dependence and seasonal-variation in respiration. Six sample trees of different sizes were selected from a completely closed canopy stand. Respiration rate r at monthly mean temperature of Kandelia obovata trees increased with increasing mass m, which tendency was described with a power function (r=f.m^h:f, multiplying coefficient; h, scaling exponent). The h values ranged from 0.723~1.085. In the cool dormant season, the h was close to 1.0, while in the warm growing season h was closer to 3/4. Respiration varied more between seasons in small-sized trees than in large-sized trees. Since almost whole leaf consists of living tissues and showed two-dimensional horizontal growth, the respiration of leaves was most likely proportional to their mass or surface area. The woody organs showed three-dimensional growth and the proportion of non-living tissues increased with increasing tree size. Hence, the respiration of woody organs might be proportional to their surface area, but not mass. So, separate measurement for respiration of leaf and woody organs are suggested to well-understand the size-dependence of respiration.