The purpose of this study is to compare catalase activity of the healthy paulownia tree with that of the diseased tree affected by witches'-broom, and to find some explanation on the abnormal metabolism of the diseased tree. Catalase activity was determined by the Warburg micro-manometric method. The results were as follows: 1) Catalase of leaf sap centrifuged with low speed (3,000 r. per min.) for ten minutes became less active than that of crude filtered sap: 1:4 with the healthy leaf sap and 1:2 with the diseased leaf sap. 2) Observations of the seasonal changes of catalase activity showed that it was smaller in the diseased leaf than in the healthy ones at the rate of 47:100 in July, 28:100 in August, 32:100 in September, 27:100 in October. The maximum activity of catalase of the healthy leaves was obtained in August, while that of the diseased ones in July. 3) Among catalase activities of leaf blades, petioles, shoots and roots, the strongest was that of leaf blades. With respect to the heathy tree catalase activity of the petioles was 8.7 per cent, the shoot was 8.4 per cent, and the roots was 1.5 per cent of that of the leaf blades. As to the diseased tree catalase activity of the petioles was 58.6 per cent, the shoots was 42.5 per cent, the roots was 8.7 per cent of that of the leaf blades. These tendencies show the difference between the catalase distribution of the diseased tree and that of the healthy one. Catalase activity of the diseased tree was greater in petioles by 77 per cent, in shoots by 32 per cent and in roots by 56 per cent than each part of the healthy tree, while in leaf blades it was vice reversible and catalase activity of the diseased tree decreased to 27 per cent of that of healthy tree. It is concluded that a large part of catalase is contained in the chloroplasts, because the leaf sap is incurred a great loss of catalase activity through the low speed centrifugation, and because the diseased leaves show a very decreased catalase activity and contain a small quantity of chlorophyll, that was mentioned by the author.