Oxyfluoride glass and glass ceramics codoped with Er3+/Yb3+ ions of the same composition were prepared. Nanocrystals in the glass ceramics were formed,characterized by xray diffraction and fluorescence spectra. The measurements by using the differential thermal analysis and the crystal parameter calculation by JuddOfelt theory indicated that the rareearth ions have entered the nanocrystals. At the same time, the ratio of the nanocrystalline phases in glass and glass ceramics before and after annealing was calculated respectively.