Abstract: To study the effects of inorganic nitrogen (inorganic-N) combined with amino-acid nitrogen (glutamic acid, Glu) on the growth and relevant enzyme activities of tobacco seedlings, water culture experiment was conducted on cv. NC55 under asepsis condition to determine the root morphology, chlorophyll and carotene contents, and activities of key enzymes related to nitrogen metabolism of tobacco seedlings. Six treatments were set at different nitrogen forms and the same nitrogen concentration:NH₄⁺-N (T1), NO₃^--N (T2), Glu-N (T3), NH₄⁺-N:Glu-N=1:1 (T4), NO₃^--N︰Glu-N=1:1 (T5) and NH₄NO₃-N:Glu-N=1:1 (T6). The results showed that the total length, surface area and total volume of roots and the length of first lateral root in T3 were the highest and the total root length in T6 was higher. The contents of chlorophyll a, chlorophyll b and carotene in tobacco leaves in T4 were the highest. The contents of leaf photosynthetic pigments in the treatments of inorganic-N combined with Glu were higher than those in N treatments alone. The leaf glutamine synthetase (GS) activity in T3 was the highest and the leaf GS activities in the treatments of inorganic-N combined with Glu were higher than those in N treatments alone. The root glutamic-pyruvic transaminase (GPT) activities in the treatments of inorganic-N combined with Glu were obviously higher than those in N treatments alone. The leaf glutamic-oxaloacetic transaminase (GOT) activity in T6 was the lowest, and the root GOT activities in the treatments of inorganic-N combined with Glu were higher than those in T2 and T3. Glu was favorable for root elongation and lateral roots formation. Inorganic-N combined with Glu could alleviate the adverse effect of inorganic-N on root growth and improve pigment synthesis in leaves. Applying Glu could increase leaf GS activity, and inorganic-N combined with Glu could enhance root GOT and GPT activities.