Abstract: If a conductive mayenite compound having a large specific surface area is obtained, the usefulness thereof in respective applications is remarkably increased. A conductive mayenite compound powder having a conduction electron density of 1015 cm?3 or more and a specific surface area of 5 m2g?1 or more is produced by: the following steps: (1) forming a precursor powder by subjecting a mixture of a starting material powder and water to a hydrothermal treatment; (2) forming a mayenite compound powder by heating and dehydrating the precursor powder; (3) forming an activated mayenite compound powder by heating the compound powder in an inert gas atmosphere or in a vacuum; and (4) injecting electrons into the mayenite compound through a reduction treatment by mixing the activated mayenite compound powder with a reducing agent.