High-temperature glass-seals are needed to perform oxygen permeation measurements on mixed ionic-electronic conducting membranes like Ba0,5Sr0,5Co0,8Fe0,2O3-δ(BSCF), which can be used for oxygen separation from air. An interesting glass-seal to fix a BSCF membrane for these measurements is MgO - BaO - SiO2, but it is not well known yet. Therefore, this work characterizes and optimizes this glass-seal and the sealing interfaces to obtain a good and gastight connection between a BSCFhollow fiber membrane and yttrium stabilized zirconia (YSZ), which is used in the oxygen permeation set-up. The glass was investigated by dilatometry and thermal gravitational analysis combined with differential scanning calorimetry. For the optimization of the sealing interfaces, different parameters of the preparation and the sealing procedure were changed such as sealing temperature, duration and the composition of the glass-seal. The characterization of the sealing interfaces was done by SEM and EDS.