A strong anisotropy is induced in melt‐spun and hot‐pressed Nd‐Fe‐B ribbons by a specific heat treatment such as a slow heating up to 1000 °C. The present study clarifies the origin of the induced anisotropy through microstructural observations. The following grain growth of Nd2Fe14B grains during heating has been observed: (I) As‐quenched Nd2Fe14B grains grow coarser at the roll side of the ribbons at around 750 °C, and at the front of the coarse‐grain region a Nd‐rich region is formed. (II) A rapid grain growth of some of the coarse grains (excessive grain growth) occurs at an interface of the two regions at around 800 °C. The grains which have theircaxes parallel to the ribbon thickness direction grow at a faster rate along a band of the Nd‐rich region. Such preferential grain growth in stacked ribbons results in the enhancement of magnetization in the press direction.