The topology and the effect of the B-content on the grain growth rate of sintered Nd-Fe-B magnets has been examined. Most of the grains have 5-6 corners. Normal grains grow slowly for B-contents <5.7 at.%, but grow faster for higher B-contents. Abnormal large grains grow almost as fast as grains in pure metals. By optimizing the composition and refining the processing route sintered Nd-Fe-B magnets with a remanence of 1.528 T, a coercivity HcJ of 840 kA/m (10.6 kOe) and a maximum energy density of 454 kJ/m3 (57 MGOe) could be prepared.