AbstractThe development of low‐cost RE‐Fe‐B sintered magnets with large La/Ce content is of great significance for the balanced utilization of rare earth (RE) resources, but it is limited by reduced magnetic properties. In this work, the coercivity (Hcj), remanence (Br), maximum energy product [(BH)max], and temperature stability are simultaneously enhanced for magnets with LaCe accounting for 40 wt% of the total RE. The synergistic regulation of the REFe2phase, Ce‐valence, and grain boundaries (GBs) in RE‐Fe‐B sintered magnets is realized for the first time by introducing appropriate La elements. The La elements inhibit the generation of the REFe2phase and tend to stay in the triple junctions, promoting the segregation of the RE/Cu/Ga elements and contributing to the formation of Ce/Nd/Cu/Ga‐rich continuous thicker lamellar GBs, and as a result, weakening the detrimental effect on HA caused by La element substitution and enhancingHcj. In addition, partial La atoms entering the RE2Fe14B phase are beneficial for improving theBrand temperature stability of the magnets and promoting the Ce3+ion ratio, which also provides additional benefit forBr. The findings provide an effective and feasible way to co‐enhance the remanence and coercivity of RE‐Fe‐B sintered magnets with high Ce content.