Abstract: In order to improve the stability of calciferol in an emulsion type injection, calciferol and calciun levulinate injection, the effects of oil medium, aqueous phase, interfacial area, calcium ions and concentrations of emulsifiers on the stability of calciferol were investigated.Calciferol was highly stable in oil medium, but tended to be oxidized in the presence of aqueous phase or calcium ions, and in the increase of interfacial area. Among these factors, the interfacial area was found to be most important in affecting the stability of calciferol.The extent of oxidation of calciferol increased with increasing concentrations of the emulsifiers used.The incorporation of butyl hydroxy ahisol and filling the ampule space with nitrogen gas were effective in improving the stability of calciferol in the emulsion type injection.