Abstract: Absicsic acid (ABA) as a kind of stress hormone has been applied to enhance a plant's resistance to various abiotic stresses, but the effect of ABA on sub-optimal temperature stress has not been clarified. The effects of ABA pretreatment on two cultivars of cucumber seedlings (chilling sensitive Jinyan 4 and chilling tolerant Zhongnong 27) under chilling stress were investigated. The cucumber seedlings were pretreated with 200 μmol/L ABA or water for 12 h, then divided into two groups and cultivated separately in two phytotrons with temperatures 25/18℃ and 10/10℃ (day/night) for seven days, respectively. The level of electrolyte leakage, the tissue water content (TWC), the chlorophyll content, the antioxidant enzyme activities and the transcriptional levels of the genes encoding these enzymes were measured. The results showed that the level of electrolyte leakage was increased under chilling stress, whereas the TWC and chlorophyll content was decreased. The activities of peroxidase (POD) and superoxide dismutase (SOD) were increased, whereas the catalase (CAT) activity was decreased under chilling stress. Pretreatment with ABA alleviated the changes of physiological features in cucumber seedlings upon chilling stress. The CAT gene transcriptional level was down-regulated and the SOD gene transcriptional level was up-regulated under chilling stress. Pretreatment with ABA also mitigated the changes of gene expression. It demonstrated that ABA may play a role in alleviating the harm of chilling stress by balancing the production and scavenging of reactive oxygen species (ROS) in cucumber seedlings. The results will provide a reference for the application of ABA to enhance the resistance of cucumber to low-temperature stress.