The study was carried out at Manko Wetland, Okinawa Island. Aboveground nighttime respiration of Kandelia obovata Sheue, Liu & Yong trees was measured monthly throughout a year to determine the respiratory behavior of mangroves in the field; to detect the dependence of respiration rate of individual trees on their size and finally to investigate the seasonal change in size-dependence of the aboveground nighttime respiration. Six K. obovata sample plants of different sizes were selected for the seasonal measurement of nighttime respiration. The respiration of the sample trees was nondestructively measured with an enclosed standing tree method under the field conditions. Respiration of K. obovata trees increased dependently on their size. The size-dependence of respiration rate r was described by a power function (r = g x m^h) of aboveground mass m. The exponent value h decreased with increasing seasonal temperature, whereas ln (g) value increased with increasing seasonal temperature.