MM85Cu15 (MM=La, Ce, Pr, Nd) eutectic alloys were added into the hot-deformed Nd-Fe-B magnets to enhance the coercivity. It is found that three endothermic peaks occur on the differential scanning calorimetry curve of the MM-Cu melt-spun ribbons at 432.2, 451.1 and 516.5 ℃. The peaks substantially correspond to three types of MM-Cu low-melting eutectic phase. The coercivity of magnets increases when the MM-Cu content is lower than 4 wt％, and then keeps almost no change with the content further increasing to 5 wt％. The coercivity of the hot-deformed magnets with 4 wt％ and without MM-Cu addition is 948 and 683 kA/m, respectively. Nearly all the platelet-shaped grains are isolated by the thickened intergranular phase after MM-Cu addition. Moreover, the average grain size of the magnets with MM-Cu addition decreases compared with that of the magnet without MM-Cu addition. Scanning electron microscopy images show that the areal fraction of the RE-rich grain boundary phase increases from 8.6％ to 15.1％ after MM-Cu addition. The La, Ce together with Cu and Ga aggregate at the grain boundary regions separating neighboring grains and smoothing the grain boundaries. Therefore, both the thickened grain boundary and decreased mean grain size result in the enhancement of coercivity after MM-Cu eutectic alloy addition.