Nitrogen is one of the most limiting elements for plant growth. Although nitrogen dynamics in mangrove forests are well understood at the ecosystem level, the plant physiological responses to nitrogen condition are less clear. The aim of this study was to analyze in detail the mangrove root respiratory responses to different nitrogen conditions. We cultivated propagules of Bruguiera gymnorrhiza, which is one of the typical mangrove plants, under nine different nitrogen conditions, and then compared root respiratory properties. The rate constant of root respiration increased in accordance with enrichment of ammonium concentration while it was not affected by nitrate concentration. This mangrove plant root seems to reduce oxygen under ammonium rich condition probably due to extra electron supply from the ammonium. The frequency factor for the reaction tended to be higher under ammonium rich condition. This leads to an interpretation that number of mitochondria and/or oxygen accessibility to the mitochondria matrix is a factor in the root respiration rate differences in this plant. Observing the overall activation energy for the oxygen reducing reaction varied from 43 to 71 KJ mol^-1 among the growth conditions, electron pathway of the root respiration chain thus might be changed according to the nitrogen conditions.