The glass structure, wetting behavior and crystallization of BaO–Al 2 O 3 –B 2 O 3 –SiO 2 system glass containing 2–10mol% Al 2 O 3 were investigated. The introduction of Al 2 O 3 caused the conversion of [BO 3 ] units and [BO 4 ] units to each other and it played as glass network former when the content was up to 10mol%, accompanied by [BO 4 ]→[BO 3 ]. The stability of the glass improved first and then decreased as Al 2 O 3 increased from 2 to 10mol%, the glass with 5mol% Al 2 O 3 being the most stable one. The wetting behavior of the glasses indicates that excess Al 2 O 3 leads to high sealing temperature. The glass containing 5mol% Al 2 O 3 characterized by a lower sealing temperature is suitable for SOFC sealing. Al 2 O 3 improves the crystallization temperature of the glass. The crystal phases in the reheated glasses are mainly composed of Ba 2 Si 3 O 8 , BaSiO 3 , BaB 2 O 4 and BaAl 2 Si 2 O 8 . Al 2 O 3 helps the crystallization of BaSiO 3 and BaAl 2 Si 2 O 8 .