We measured bidirectional N transfer and quantified the amount of transferred N between Eucalyptus urophylla × grandis (Eucalyptus) and Dalbergia odorifera (Dalbergia), to determine whether the facilitation process from N transfer could improve Eucalyptus productivity and nodulation of Dalbergia. A 15N leaf-labeling study was conducted by using a pot experiment with Dalbergia and , and 15N was traced in the labeled species as well as in neighboring trees at 90, 135 and 180 days after labeling. Bidirectional N occurred between Eucalyptus and Dalbergia, the amount of net transferred N was 21.8–127.0 mg plant-1 N from Dalbergia to Eucalyptus, which was equal to 1.5–21.2 % of the total N accumulated in Eucalyptus plants to increase the biomass of Eucalyptus. The results also showed that the nodule number of Dalbergia increased by 19.4–107.4 % in the intercropping system and further improved its N2-fixation. The concentration of soil nitrogen, especially the concentration of N-NH4+, was a major factor affecting N transfer in this system. This study indicated that the advantage in Eucalyptus and legume intercrops relates to ‘complementary N use’, which provide a significant amount of N required for Eucalyptus productivity, and maintain ecological sustainability.