12SrO•7Al₂O₃ (S12A7) is a meta-stable phase in the system of SrO-Al₂O₃ and has the isostructure with 12CaO•7Al₂O₃ (C12A7), which is composed of sub-nanometer-sized cages with oxygen ions loosely encaged in the cages. This letter reports fabrication of polycrystalline thin films of insulating and metallic S12A7 electride thin films. The as-crystallized film was an electrical insulator, while light-induced persistent electronic conduction with a conductivity of~1×10^-3 S•cm^-1 at 300 K was realized in proton-implanted films. Higher conductivities of~270 S•cm^-1 were attained in the films subjected to a reduction treatment using an oxygen deficient amorphous film deposition. These behaviors are similar to those observed on C12A7. The present results suggest that S12A7 is another candidate material to explore electronic functions originating from a nanoporous structure embedded in a crystal structure.