Abstract: Nutrient solution hydroponics was adopted to study the effects of exogenous proline on nitrogen reduction in the leaves and roots of "xuemei" melon(Cucumis melo L.) seedlings under NaCl stress.The results shown that:(1)Salt stress increased the NH₄⁺-N and soluble protein content in leaves and roots of melon seedlings;and decreased NO₃^--N content and nitrate reductase(NR) activity;and(2)Exogenous proline increased NO₃^--N and soluble protein content in leaves and roots of melon seedlings under salt stress;decreased NH₄⁺-N content;and increased NR activities.These results indicated that exogenous proline could ease injury suffer when melon seedling experience salt stress relying on adjusting NR activity and nitrogen compounds contents.