In this work, the effects of Ge addition on the microstructure and magnetic properties of some rapidly quenched Nd_13.5Fe_(74.9–z )Co_5.5Ge_z B₆ alloys with z = 0.0, 0.18, 0.36, 0.54, 0.72 and 0.9 prepared by a rapid solidification method were studied. For the first time, detailed microstructural study of nanometer size grain boundaries enriched with very small amount of Ge as well as Nd was carried out using 3 Dimensional Atom Probe (3DAP) technique. The magnitudes of B _r and (BH )_max were seen to increase for the samples substituted with up to 0.36 at% Ge in spite of the fact that Ge is a non‐magnetic atom. This was related to the observed change of Co concenteration in matrix phase. However, the magnetic properties deteriorated for the samples with Ge addition beyond 0.36 at%. The observed magnetic properties are discussed in relation with the observed microstructural changes monitored by 3DAP and …