Abstract: The effect of calmodulin antagonist W7 on antioxidant systems of roots of cucumber seedlings under hypoxia stress was studied in hydroponics culture. Results show that pretreated seedlings with calmodulin antagonist W7 under hypoxia stress have lower SOD, POD, CAT, APX and GR activities, and higher production rate of O₂^-, MDA and H₂O₂ contents compared with hypoxia stress treatment without calmodulin antagonist W7 pretreatment. This indicates that calmodulin antagonist W7 pretreatment can restrain Ca²⁺·CaM signal transduction, leading to increase in reactive oxygen content and decrease in activity of certain antioxidants, subsequently reducing resistance of cucumber seedlings to hypoxia stress, hence stunted roots. The experiment shows that Ca²⁺·CaM signal system plays an important regulating role in alleviating hypoxia stress in roots of cucumber seedlings.