Distribution of D-amino acid oxidase was studied with the tissues of dog, rat, pig, cow, horse, guinea pig, rabbit and cat. The enzyme activity was measured both with the homogenates of these tissues and the enzyme samples purified from the homogenates. The results showed that the distribution of this enzyme was restricted to the kidney, liver and brain. In every animal, the amount of the enzyme in the kidney was larger than that of the liver, and the small amount was found in the brain. The order of the concentration of this enzyme in the kidney is as follows : pig>rat>dog>cat>horse>cow>guinea pig>rabbit.