1. Conditions of preparation and purification of superoxide dismutase from hog liver and erythrocytes were established. 2. The enzymes from both tissues were compared in respect to electrophoretic mobility, pI value, amino acid composition and spectrophotometric profiles and some differences were observed. 3. Conditions of enzyme dissociation were elaborated and molecular weights of subunits obtained from both kinds of SOD were found to be approx. 16,000. 4. Effect of heat and pH on the enzyme activity were tested. Both enzymes exhibited a relative thermostability.