Glassy microspheres containing a rare earth are attractive for practical use as microcavities for morphology-dependent resonances (MDRs). However, no efficient and low-cost mass-production process has been established for such microcavities. In the present study, we have synthesized glassy microcavities through liquid-liquid phase separation of alkaline-earth borate glass. Glassy microspheres have been prepared by the liquid-liquid phase separation of BaO-B2O3. glasses, by controlling the particle size within the range 1-45 mum and the size distribution within 1%. The microspheres show periodic, sharp peaks, indicative of MDRs, in their Raman-scattering spectra and in the fluorescence spectro the internal rare earth. These microspheres act as high-quality microcavities, with Q factors comparable to those calculate using the Lorenz-Mie theory.