The author had the experiment infusing the several kinds of monosaccharide (glucose, xylose and galactose) to the intestinal canals of rats and investigating the influence of Vitamin B(2) upon the absorption of monosaccharide and obtained the following results: 1) The young animals have increased their weight by the injection of the proper quantity of Vitamin B(2). In this case, the rate of increase was proportionated to the quantity of injected Vitamin B(2). 2) Owing to the injection of the proper quantity of Vitamin B(2), the absorption index of glucose to the rat's intestinal canal became to rise. In this case, the rising rate was proportionated to the quantity of the injected Vitamin B(2). 3) Owing to the injection of the proper quantity of Vitamin B(2), the absorption index of galactose to the rat's intestinal canal became to rise. In this case, the rising rate was proportionated to the quantity of the injected Vitamin B(2). 4) The absorption index of xylose to the intestinal canal has no relation with the injection of Vitamin B(2). This can be said because the absorption of xylose (pentose) is difference with that of hexose as glucose, galactose and etc.