A pot experiment was performed to study the drought resistance of Eucalyptus grandis Hill ex Maiden saplings under different nitrogen(N) application levels.The experiment consisted of two steps,firstly three N treatments (N₀,supplied no extra urea,and N₁ and N₂,supplied urea 1.4 and 2.8 g·pot^-1,respectively) were carried out in advance for 20 days and afterwards the drought stress[continuous drought for 0 d(D₀),3,6,9,12,15 and 18 d)] was conducted respectively to each N treatment.The results showed that:(1)Under the drought condition,the leaf water content (LWC),leaf relative water content (LRWC) and leaf water retention (LWHC) of saplings in N₁ and N₂ were lower than those in N₀ level,and the differences in the middle stage of drought were most obvious,which indicated that nitrogen application before drought probably led to negative impact to leaf water physiology of E.grandis saplings.(2)As for the soluble protein (SP) and soluble sugar (SS),the differences between nitrogen treatments were not significant in the early days of drought,but when drought for 9 ~ 18 d,the increase of SP and SS in N₀ were more obvious than those in N₁ and N₂,and the change trend of those in N₁ and N₂ were relatively gentle,indicating that nitrogen addition was adverse to the accumulation of SP and SS of E.grandis saplings.However the increase rate of proline (Pro) in N₁ and N₂ was higher than that in N₀ with the extension of drought.(3)With the aggravation of drought stress,the contents of H₂O₂ and MDA in E.grandis saplings in treatment N₁ and N₂ were obviously higher than those in treatment N₀,which indicated that nitrogen addition brought about more serious water deficiency of E.grandis saplings and produced more reactive oxygen species (ROS).(4)Nitrogen addition did not significantly change SOD activity and AsA content of E.grandis saplings in the process of drought stress,but POD activity in N₁ and N₂ was obviously higher than that in N₀.(5)Nitrogen addition increased the pigment content of E.grandis saplings and kept at a higher level and correspondingly the net photosynthesis rate(P_n) was at a high level at the beginning of drought stress (0~3 d),but with drought time prolonged,P_n declined more rapidly,and change trend of transpiration rate (T_r) and Stomatal conductance (G_s) were nearly same as P_n.The results suggested that nitrogen addition could enhance the photosynthesis and assimilation ability of E.grandis when soil moisture is sufficient,and promote its growth.However it is more likely to encounter water deficit in face of drought stress and reduce its ability to drought resistance.Thus in the process of management of E.grandis plantation,nitrogen addition should not be implemented before the coming of drought or seasonal drought.Otherwise irrigation or some watering measures should be taken.