This paper presents a determination method for vitamin A esterase activity of animal tissues. Vitamin A esterase activity was recognized in the liver homogenate and pancreas acetone powder incubated at 38℃ for 30 minutes at pH 8.5. A decrease of vitamin A was observed during incubation, but was prevented by the addition of 2 mg of α-tocopherol and 1 mg of ascorbic acid for 100 mg of liver. On determining vitamin A esterase activity, the amount of vitamin A acetate had no effect on the esterase activity when less than 500 I.U. but that of Tween 80,a suface active agent, exerted some effects.