In the process of medical care of acute diarrhea in children, two pathophysiologic aspects should be considered: dehydration associated with electrolyte imbalance, and nutritional disorder. It is important to continue to provide foods easy to digest with appropriate recipes from the early stage after a remedy of dehydration using oral rehydration solution or intravenous fluid therapy according to patients' condition. Nil per os or diluted diet can slow the recovery of an intestinal function and lengthen the diarrheal period. Although the damage on the intestinal mucosa occurs from various causes, the gastrointestinal mucosa maximizes absorbing capacity by expanding the area of a surface. Early oral-feeding contributes to restoring mucosa favorably and thus facilitates a rapid improvement of symptoms. Breast-feeding should continue to be performed in the midst of rehydration, and lactose-containing regular cow's milk formula is recommended for cow's milk-fed patients after rehydration. In mild or severe acute diarrhea, administering probiotics in conjunction with feeding is expected to shorten the diarrheal period.