Abstract The effects of cyclic heat treatment and cooling rate on the coercivity and microstructure of sintered Nd 15Fe 77B 8 magnet have been investigated. Upon cyclic heat treatment, the coercivity variation is almost reversible depending on the cooling rate after each heat-treatment cycle. The as-sintered and slowly cooled (4.5 °C min −1) magnets showed a low coercivity of about 334 kA m −1, while the rapidly cooled (about 200°C min −1) magnets exhibited a high coercivity above 653 kA m −1. Both transmission electron microscopy (TEM) and X-ray diffraction analyses have revealed that the magnets with high coercivity contain an increased amount of the d.h.c.p. Nd-rich phase.