The changes in alkaline phosphatase activity during development in Rana catesbeiana were examined by electrophoresis and spectrophotometry in embryos and hatching and hatched tadpoles, and in various visceral organs, such as the liver, pancreas, kidney and intestine of tadpoles and froglets. Alkaline phosphatase first appeared at the hatching tadpole stage. The liver showed the first band of alkaline phosphatase at st. III. This band migrated at 2.3∿2.4cm from the origin. A new band having a mobility of 2.1cm appeared at one month after st. XXV. The activity of this enzyme became low at st. XIX, and then increased. In the pancreas, a band having the same mobility as the first band of the liver appeared at st. III and remained in all subsequent stages. Activity was high at st. XIX and after st. XXIII. In the kidney, a band migrating at 1.3∿1.4cm appeared at st. III and existed in all the subsequent stages. Activity was high at st. XIX and again at one month after st. XXV. In the intestine, the first band of 2.0∿2.1cm in mobility appeared at st. 24∿25 and was replaced by the second band of 1.6cm in mobility which appeared at st. XXIV or XXV. Activity was high at st. XIX and also at st. XXIV or XXV.