Provided is a method for preparing an electroconductive mayenite type compound with good properties readily and stably at low cost without need for expensive facilities, a reaction at high temperature and for a long period of time, or complicated control of reaction.A method for preparing an electroconductive mayenite type compound comprises a step of subjecting a precursor to heat treatment, wherein the precursor contains Ca and/or Sr, and Al, a molar ratio of (a total of CaO and SrO:Al.sub.2O.sub.3) is from (12.6:6.4) to (11.7:7.3) as calculated as oxides, a total content of CaO, SrO and Al.sub.2O.sub.3 in the precursor is at least 50 mol %, and the precursor is a vitreous or crystalline material; and the method comprises a step of mixing the precursor with a reducing agent and performing the heat treatment of holding the mixture at 600-1,415.degree. C. in an inert gas or vacuum atmosphere with an oxygen partial pressure of at most 10 Pa.