Stomach and intestinal contents of eel leptocephalus are largely composed of amorphous substance. What kind of food do they eat, and how do they digest and absorb the nutrient from the food to make their unique form filled with amorphous substance in the body? Before the commencement of artificial feeding, forced administration of protein solution into the stomach of elvers resulted in a rapid increase of the protein in the blood plasma. However, the protein transport into the blood decreased with the development of digestive ability. The results, on the contrary, indicate that eel larva before metamorphosis, i.e., leptocephalus, has less digestive ability.