Through the hepatic glycogenolysis is the most important metabolism for energy source, the hormonal regulation in neonate is unknown yet. The neonatal rats were investigated chronologically in regard to liver wet weight, blood glucose, liver glycogen, liver glucose and liver cyclic AMP. And the influence of epinephrine and glucagon on the glycogenolysis were observed using isolated perifused rat liver. As a result, following conclusions were drawn. 1. In the earlier neonate, the source of the blood glucose mainly depended on the liver glycogen restored before birth. In the later neonate, the liver glycogen was reaccumulated by the progression of the suckling. 2. Although, in the earlier neonate, the influence of epinephrine on the glycogenolysis was more dominant than that of glucagon, the hepatic glycogenolysis was completely established by both hormones since the fifth day from birth. 3. In respect to the glucose output of liver, it was regulated by the interaction of these two hormones chronologically. 4. In the hepatic glycogenolysis of the neonates, just like that of the adults, cyclic AMP was also the second messenger of epinephrine and glucagon. 5. The third day after birth in the neonate was the critical period in the carbohydrate metabolism.