Abstract: The effects of exogenous 24-epibrassinolide (24-epiBR) on time dependent changes of activities of major antioxidant enzymes (superoxide dimutase, SOD; peroxidase, POD; catalase, CAT), lipid peroxidation, soluble protein and heat shock protein(HSP) contents of cucumber Seedlings in hypoxia-resistant cultivar were studied in this paper. Compared to seedlings treated with "hypoxia stress", the activities of SOD and POD increased in both cultivars treated with "hypoxia + 24-epiBR". There was no significant difference in CAT activity between the "hypoxia stress" treatment and "hypoxia +24-epiBR" treatment. Lipid peroxidation level was significantly increased in seedlings exposed to hypoxia stress but decreased with exogenous 24-epiBR application. In contrary to seedlings treated with "hypoxia stress", soluble protein and HSP contents were enhanced in seedlings treated with "hypoxia +24-epiBR", and soluble protein contents were higher than those of the control. The results suggest oxidative damage that occurs in seedlings under hypoxia-stress conditions is considerably alleviated by 24-epiBR treatment.