Vitamin A esterase activity of several tissues and blood of rat was investigated. Optimum pHs of the activity were 8.5,9.0 and 9.7 for the enzymes of the liver and pancreas, for those of the kidney, lung and intestine, and for those of speen and muscle, respectively. Vitamin A-acetate was hydrolyzed with every tissues and blood. Vitamin A-palmitate was hydrolyzed only with the pancreas, but not with any other tissue or blood. The activity of the pancreas and liver was high, and especially that of pancreas highest, but that of the other tissues low. The esterase activity in blood was found to be present not only in erythrocyte but also in leucocyte, but not in the plasma and serum.