Mayenite (12CaO·7Al2O3, C12A7) electride with an anti-zeolite nanoporous structure has attracted intense attention due to its versatile promising application potentials. However, the synthesis difficulty because of extremely harsh conditions (e.g., reduction in sealed calcium or titanium vapor) significantly obstructs its realistic applications. In this work, we employed a simple, efficient, and cost-effective route for synthesizing mayenite electrides (C12A7:e-) in both powder and dense ceramic. C12A7:e- powders with efficient electron doping (3.5 × 1020 cm-3) were obtained via simple graphite reduction of a novel mixture precursor of CaAl2O4 (CA) and Ca3Al2O6 (C3A) derived from a modified Pechini method. The structural evolution during the electride formation was investigated, and it was found that reduction below 1300 °C induced the formation of Ca5Al6O14 (C5A3), while reduction above 1400 °C helped retain the mayenite structure. Fully dense C12A7:e- ceramics were also fabricated via graphite reduction of presintered pellets with a relative density of 97.9% starting from the CA+C3A mixture. Careful studies improved the mechanism cognition of graphite treatment that the electrons injection was probably initiated by surface reduction with involatile C species (e.g., C22-) rather than previously proposed CO, during which the mixed conduction of oxygen ions and electrons played an important role. Furthermore, the stability of C12A7:e- in water as well as in the presence of moisture was discussed. These results not only suggest a novel precursor for fabricating high-quality mayenite electrides but also provide in-depth insights into the stability of the mayenite structure toward practical applications.