Fructooligosaccharides (FOS) are well known as prebiotics which improve intestinal microflaura. FOS also have increasing effect on the intestinal absorption of calcium (Ca), magnesium (Mg) and iron. These effects were inspected by many animal experiments and then by human studies. Especially, FOS clearly prevent the decrease of bone mineral density by gastrectomy in rats. In this report, we mainly explain the preventive effect of FOS on the bone of gastrectomized rats and introduce relationship between another food ingredient or exercise.