Abstract: The characteristics of E. crassipes leaf SOD in reiation to low temperatue,pHand physiological age were investigated.SOD activity was nearly unaffected whenenvironmental pH changed within a narrow range,but declined markedly when pHchanged remarkablely.After the leaves of E. crassipes were exposed to a low temperature of 2℃ for 4,8,12,16 and 24 hours,the SOD activity decreaed obviously.But the number of SOD isoenzyme bands remained unchanged though the activitiesof the bands changed.As the senescence of the leaves continues,SOD activity decr-eases gradually.Both the SOD activity and the number of SOD isoenzyme bands aremuch higher in the young leaves than those in the senesced leaves.