Abstract: A hydroponic experiment was conducted to study the effects of 24-epibrassinolide (EBR) on the isozyme expressions of aerobic respiration enzymes in cucumber seedling roots under hypoxia stress. Hypoxia stress promoted the isozyme expressions of root isocitrate dehydrogenase (IDH), succinate dehydrogenase (SDH), malate dehydrogenase (MDH), and malic enzyme (ME), and produced several new bands. Applying 10 ^-3mg·L^-1 of EBR under hypoxia stress increased the isozyme expressions of IDH and MDH on day 6 and day 9 by 52.8% and 13.6%, and 39.1% and 11.3%, respectively and the isozyme expressions of ME on day 3 by 11.6%, but decreased the isozyme expressions of SDH on day 6 and day 9 by 42.9% and 36.1%, respectively, as compared with those under hypoxia stress alone. These results indicated that applying EBR under hypoxia stress could regulate the isozyme expressions of IDH, SDH, MDH, and ME in cucumber seedling roots, and thereby, alleviate the damage of hypoxia stress on the seedling roots.