The effect of a high magnetic field on coercivity was investigated in the annealing process for sintered Nd- Fe-B magnets containing Dy 10 wt.%. In a sample containing Cu 0.13 wt.%, a coercivity value H_c of 36 kOe was obtained for an annealing temperature T_a of 475°C under an annealing field H_a of 140 kOe. This value of H_c is 20% larger than that for the control sample (T_a = 475°C and H_a = 0). In samples without Cu, H_c values were considerably smaller (< 27 kOe) and no such enhancement of the coercivity by the magnetic fields was observed. The DSC curves exhibited a marked endothermic reaction just below 500°C only for samples containing Cu. This temperature is attributed to a eutectic point of Nd₇₀Cu₃₀. A possibility of field-induced alignment of Nd-rich grains in a matrix of Nd-Cu liquid is discussed; this would be closely related to the coercivity enhancement.