The purpose of the present paper is to study the influence of glass composition on the thermal stability in the system, and three glasses were consequently investigated. Although Glass A has a coefficient of thermal expansion (CTE) that shows the best match with those of anode and electrolyte materials of solid oxide fuel cells (SOFCs), the thermal stability of Glass A is quite poor, where after being heat treated at for only , the CTE of the glass increased more than 24%. The change of the CTE value was mainly attributed to the fast crystallization that formed high CTE value phases such as and . In order to improve the thermal stability, BaO in Glass A was replaced by (Glass B) and (Glass C). It was found that the decrease in the BaO content improved the thermal stability of the resultant glasses. Glass B showed less than 8% change of the CTE during annealing time at , while Glass C exhibited superior long-term thermal stability, where the change of the CTE was within the equipment detection limit after being heat treated for at . The good thermal stability of Glass C was believed to be due to the formation of a more compact glass network after the substitution as compared with that of Glass A. The good thermal stability makes Glass C attractive to be used as the sealing material for SOFC applications.