The various organs of the rat such as the heart, kidney, liver, spleen, lung, brain, stomach and intestines have been observed by applying the method for non-specific ATPase devised by Wachstein, which means that the ATPase is resistant to the formol calcium fixation and, is activated by magnesium ion at pH 7.2. As the result the following conclusion were obtained: 1). In each tissue the strongest positive reaction is demonstrated on the blood vessels, artery and venous blood capillaries, and on the smooth muscle. 2). In the liver the bile canaliculi gave a strong positive reaction, in the kidney the brush border of urinary channels and gromeruli, in the intestines the surface of mucous membrane and the central chyle vessels, and in the lung a slightly positive reaction in alveolar cells and strong positive reaction in the smoot muscle of bronchi and of blood vessels. 3). In the brain the stongest positive reaction was observed in capillary vessels, and in the spleen the inner surface of sinusoid, the intercellular space of reticlum cells and of those in the germinal center; while lymph follicule gave the negative reaction. 4). This ATPase reaction is not inhibited by PCMB and not accelerated by L-cystein added in media but the activity is lost gradually by incubating with calcium formol at room temperature. 5). The activity of this tye of ATPase has been discussed with the special referenc to the permeability of the cell membrane.