Glycine incorporation into rat intestinal mucosa was observed in vitamin D deficient male rat (U.S.P. rachitogenic diets, No. 2,for over 4 weeks) or vitamin D fed rat (2,000 I.U. of D_3 was administrated orally 27 hours before sacrification). 20 μmoles of glycine-1^<14>C (2.15 c/mole) was injected peritoneally 3 hours before the sacrifice. Increases of glycine-1^<14>C incorporation with D_3 administration was observed into the microsomes and supernatant fractions of rat intestinal mucosa cells, and into the lipid, protein and RNA fractions. In microsomes glycine incorporation into lipid and protein was also increased with D_3 administration. These stimulating effect of D_3 was further observed in the intestinal mucosa incubated with glycine-1^<14>C (in vitro). On these results, D_3 administration would cause to stimulate the formation of RNA, and then induce the formation of protein and phospholipid in rat intestinal mucosa.