The phase diagram of a cetyltrimethyl ammonium bromide (CTAB)/n-butanol/n-octane/KNO3-Mg (NO3) 2 system was drawn. Nanoparticles of Eu2 + -doped KMgF3 were prepared from the quaternary microemulsions of cetyltrimethyl ammonium bromide(CTAB), n-butanol, n-octane and water. The X-ray diffraction(XRD) patterns were indexed to a pure KMgF3 cubic phase. The environmental scanning electron microscopic(ESEM) images show the presence of spherical Eu2 + -doped KMgF3 nanoparticles with a diameter of ca. 20 nm. The emission of KMgF3: Eu2 + nanoparticles peaks at 360 nm. The excitation band was observed at 250 nm with a blue shift of ca. 70 nm compared with that of KMgF3: Eu2+ single crystal. The preparation method of nano-KMgF3: Eu2+/PMMA composite films was inquired into.