The effects of Ge and Ga additions on the microstructure and coercivity of melt-spun ribbons of Nd_13.5 Fe_(74.9−z) Co_5.5 M _z B₆ (z=0.0 to 0.54; M=Ge, Ga) alloys have been investigated. For the first time, a detailed microstructural study of nanometer-sized Nd-rich grain boundary phase enriched with small amounts of Ga and Ge was carried out using a three-dimensional atom probe (3DAP) technique. Ga partitions to thin uniform Nd-rich grain boundary phase, causing effective isolation of Nd₂Fe₁₄B grains. As a result, the coercivity increased. On the other hand, Ge caused the formation of Ge- and Nd-rich precipitates, resulting in the formation of dispersoids along the grain boundaries. Due to the poor isolation of the Nd₂Fe₁₄B grains, the coercivity decreased.