Abstract: The composition of membranefat acid, the activity of SOD enzyme and membrane permeability in the leaves of different elite Eucalyptus dunnii were analyzed to study the cold resistance characteristics of the different elite individuals. The results indicated that the index of unsaturated fatty acid(IUFA) could be adopted to evaluate the cold resistance of the individuals, whose IUFA index varied between 187.02-231.68 among the different elite Eucalyptus dunnii plants. Treated by the low temperature stress, the activity of SOD enzyme rose with the increasing stress of lowtemperature before the inflexion and then dropped sharply after the inflexion. The membrane permeability increased quickly along with the lowtemperature stress intensified before the inflexion and increased slowly after the inflexion. The weaker the coldresistance was, the earlier the inflexion occurred. The study with different physiological indexes showed that the inflexion value of the SOD enzyme activity was in accordance with the membrane permeability. It was proposed that the lowest temperature with which the inflexion occurred for SOD enzyme activity could be taken as the threshold of coldresistance for different elite Eucalyptus dunnii individuals.