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 C upon the absorption of monosaccharide, and obtained the following results. 1) The injection of the proper quantity of Vitamin C was effective for the absorption of glucose to the intestinal canal, but the much injection did reduce the index of absorption. 2) The same action was seen at the absorption of galactose. 3) The injection of the proper quantity of Vitamin C had no influence upon the absorption of xylose. This can be said because the absorption of xylose (pentose) is difference with that of hexose as glucose, galactose and etc.