Abstract: Melon ‘Xiyu 1’ was used to investigate the effect of exogenous γ-aminobutyric acid（GABA）on the inorganic nitrogen metabolism and mineral elements contents under hypoxia stress in hydroponics culture. The result showed that the activities of nitrate reductase（NR），nitrite reductase（NiR）and the contents of nitrate（NO₃^--N），nitrite（NO₂^--N），ammonium（NH₄⁺-N），glutamic acid，amino acids，total nitrogen as well as Mn，Fe，Cu significantly increased in roots of melon seedlings under hypoxia stress，however the contents of soluble protein and K⁺，Ca²⁺，Mg²⁺，Zn obviously decreased，as a result the growth of roots was inhibited；Compared with hypoxia stress，the contents of NO₃^--N，NO₂^--N，NH₄⁺-N，glutamic acid，amino acids，soluble protein and activities of NR，NiR in roots weresignificantly increased when melon seedlings were grown in the nutrient solution of applying GABA under hypoxia stress，meanwhile the mineral elements contents in roots such as total nitrogen，K⁺，Ca²⁺，Mg²⁺，Zn were significantly increased，but the contents of Mn，Fe，Cu were significantly decreased，which relieved the inhibition of hypoxia to roots in melon seedlings. However，exogenous GABA and sodium tungstate application aggravated the harm of hypoxia stress to melon seedlings through inhibiting NR activity and decreasing contents of NO₃^--N，NH₄⁺-N，glutamic acid，amino acids，soluble protein，total nitrogen and dry weight in roots. The result indicated that exogenous GABA might alleviate the damage of melon seedlings from hypoxia stress via enhancing NR activity and improving nitrate absorption and transformation，meanwhile increasing K⁺，Ca²⁺，Mg²⁺，Zn contents and decreasing Mn，Fe，Cu contents in the roots.

Key words: melon, hypoxia stress, GABA, inorganic nitrogen metabolism, mineral element