Inorganic　[Ca24Al28O64](4+)(4e(-))　(C12A7:e(-))　has　been　directly　synthesized　by　reactive　sintering　of　CaO,　Al2O3,　and　Ca　powders　at　1200　degrees　C　in　a　vacuum　for　20　min.　The　electron　concentration　in　the　as-prepared　C12A7:e(-)　was　enhanced　up　to　2.1　x　10(21)　cm(-3)　by　simply　regulating　the　addition　amounts　of　Ca,　covering　metallic　conductivity.　The　electronic　structure　results　indicated　the　existence　of　homogeneous　trapped　electrons　in　the　lattice.　Further　thermal　analyses　illustrated　that　Ca　made　a　dual　function　of　in-situ　reducing　agent　and　significantly　decreasing　the　generation　temperature　of　mayenite　phase.　These　results　provided　a　potential　path　in　the　fabrication　of　high-quality　C12A7:e(-)　toward　massive　productions,　laying　a　foundation　for　practical　applications　such　as　electron　emission　and　catalyst　support.