The effects of Cu addition on the microstructure and coercivity (_iH_c) of melt-spun annealed ribbons of Nd_13.5Fe_(74.9−z)Co_5.5Cu_zB₆ (z=0.0–0.54) alloys have been investigated. It was observed that Cu segregates to a nano-scale Nd-rich intergranular phase, causing effective change in the chemistry and morphology of grain boundary phase. As a result, the coercivity, at first decreases (up to 0.18 at% Cu), then gradually improved with the increase of Cu concentration. The effects of the microalloyed element on the coercivity are discussed based on the magnetic and microstructural changes measured and observed by a vibrating sample magnetometer (VSM), a transmission electron microscope (TEM), and a three-dimensional atom probe (3DAP).