Abstract: The effects of K⁺ and Ca²⁺ on membrane lipid peroxidation and endogenous oxygen radicals scavenging enzymes systems under high NO^-₃ stress in cucumber seedling were studied. The results showed that cucumber seedlings stressed under same high NO^-₃ concentration for 7 d, membrane lipid peroxidation produce (MDA) increased with the increase of Ca²⁺ concentration and relative electrolytic leakage was rising when K⁺ concentration rised. So injury mechanism brought by K⁺ and Ca²⁺ on cell membrane was different. And the response of endogenous oxygen radicals scavenging enzymes system in cucumber seedlings on K⁺ and Ca²⁺ concentration was also different. To a certain extent, K⁺ and Ca²⁺ could improve the activities of SOD, POD and CAT, and protect plants against damage from free radical to strength adaptability of plants to adversity.