Provided are a ferrite carrier core material for an electrophotographic developer having a full length L1 of grain boundary and a circumference length L2 of the core material in a cross-section of the core material, and satisfying a relationship of 2≤L1/L2≤9; a carrier for an electrophotographic developer including the ferrite carrier core material and a coating layer containing a resin provided on a surface of the ferrite carrier core material; and an electrophotographic developer including the carrier and a toner.