In order to investigate the changes of NO synthesis and sucrose metabolism in melon seedlings under chilling stress, cultivar ‘Hongyou’ (chillingtolerant) and ‘XL1’ (chillingsensitive) melon seedlings were treated with 6 ℃ for 0，1，3，6，12，24 h，3 d，5 d and 7 d in climate chambers. The results showed that： （1） chilling stress increased the activity of nitrate reductase (NR) and induced NO production. The response time and change of NO to chilling stress were earlier and more obvious in chillingtolerant cultivar ‘Hongyou’. （2） Compare with the control, the chilling stress condition increased sucrose, fructose and glucose contents, enhanced the activities of sucrose phosphate synthase (SPS), sucrose synthase (SS), acid invertase (AI), neutral invertase (NI), and decreased starch content. （3） The contents of soluble sugar, soluble protein and proline in the leaves of the two melon seedlings increased under chilling stress. These results indicated that melon seedlings could respond to chilling stress by inducing NO and carbohydrate generation. In addition, the accumulation of sugar substances induced by chilling stress was later than the production of NO.