Abstract:In the KCN inhibition experiment, it was found that superoxide dismutase from the hypo- cotyl of etiolated soybean seedlings which is composed of 88% Mn-SOD and 12% Cu-Zn-SOD. Latent activity of SOD was evidently liberated after the mitochondria were treated by supersonication. Most of SOD activity was present in supernatant fraction after the supersonicated mitochondria were centrifuged at 150000 g for 60 min. The method of separation and praparation of sub-mitochondrial fraction is described in this paper, and the results indicate that the 80% of mitochondrial SOD present in mitochondrial matrix fraction and a small amount SOD (16%) present in the mitochondrial intermembrane space. The results indicate that distribution and localization of intramitochondrial SOD from higher plant tissues are similar to that from animal tissues.