Abstract: Nitrogen (N) can be transferred between plants. In order to remain N balance between plants and fertility of soil, mixture of N2-fixing plants and non-N2-fixing plants provide good system for forestry. To investigate whether the root isolation (e.g. complete isolation, partial isolation and no isolation) could account for the mixed Acacia melanoxylon and Eucalytups urophylla growth response and N transfer, the authors assessed N transfer by 15N-soil/leaf-label method in a pot study. The height, diameter and biomass of 7-month-old A. melanoxylon were lower when the root isolation reducing. By contrast, the growth index were significantly higher in E. urophylla grown under no isolation than that of grown in complete isolation, indicating E. urophylla owns stronger absorbing capacity than A. melanoxylon. In both 15N-soil/leaf-label treatments, the total 15N content of E. urophylla was significantly higher (5.0 and 59.6 times) in partial or no isolation than in complete isolation respectively. In 15N-soil-label status, the total 15N content in A. melanoxylon grown by no isolation were significantly lower than that of the other two isolation treatments. Nevertheless, by 15N-leaf-label, A. melanoxylon in complete isolation had significantly lower total 15N content than the other isolation treatments. Irrespective of the labeled status, A. melanoxylon always transferred the N to neighbor E. urophylla. The percentage and amount of N transfer increased with the root isolation reducing.