Abstract: Seedlings of summer squash were sprayed on leaves with different concentration levels of exogenous salicylic acid. Effect of SA on relative electric conductivity， soluble sugar content， CAT activity， free water/bound water ratio in summer squash leaves under low temperature stress （15℃ and 5℃） were studied. The results showed that relative electric conductivity and free water/bound water ratio in summer squash leaves were decreased， soluble sugar content and CAT activities were increased in treatments of different concentrations of SA， which indicated that exogenous salicylic acid can relieve low temperature stress of summer squash seedlings. The treatment of 250 mg·L-1 SA had the best effect on relieving 5℃ low temperature stress of summer squash seedlings，but the treatment of 350 mg·L-1 SA had the best effect on relieving 15℃ low temperature stress of summer squash seedlings.

Key words: summer squash, low temperature stress, salicylic acid