Due to a high-oxide ion conductivity, strontium and magnesium co-substituted lanthanum gallate (LSGM) is considered as a potential electrolyte material for solid oxide fuel cells. Aluminium substitution for gallium in LSGM increases the bulk oxide-ionic conductivity, with added thermodynamic stability and lower cost. The objective of the proposed work is to investigate the high-temperature crystal structure of Al3+-substituted LSGM in order to explain the observed conductivity enhancement.