Under solution culture, used Cu-tolerant cultivar 89112 and sensitive cultivar Shuang-70 of Nicotiana labacum L. as plant material, five Cu levels (0, 0.5, 1, 5, and 10 mg?L- 1) were applied to study the effects of copper on nitrogen metabolism. The results showed that with the increase of Cu concentration, the contents of NO-3 -N in two Nicotiana tabacum cultivars were increased firstly and then decreased, and the NO-3 -N contents in 89112 were higher than in Shuang-70. The negative effects of Cu on the assimilation of NO-3 -N were increased with the treated length., The activities of GS and GOGAT were increased firstly and then were inhibited by the increased Cu. Then, as the treated length prolonged, the inhibitory effects were increased. In constrast to Shuang-70, the enzyme activities were higher in 89112, implicating that the 89112 is more tolerant to high Cu stress. At low Cu lever, activity of glutamate-pyruvate transaminase (GPT) was increased, and content of the free amino acids was reduced. The decline of the free amino acid contents in Shuang-70 was more rapidly. Compared with the control, protein content was increased by Cu stress. In short, it is indicated that Cu stress may enhance nitrogen transformation metabolism in Nicotiana tabacum L. seedling.