Abstract To investigate the dependence of intrinsic coercivity of R-Fe-B permanent magnets (R = rare earths) on the anistropy field of R 2Fe 14B, the temperature dependence of the intrinsic coercivity of Pr 15Fe 77B 8 and Nd 15Fe 77B 8 have been measured from 4.2 K to the Curie temperature of the magnets. Study of the interrelation between coercivity and anisotropy field by modifying the anisotropy field through atomic replacement in the rare earth sublattice has been also attempted in pseudobinary alloys (Nd 1− x R′ x ) 15Fe 77B 8 with R′ = Tb, Dy and Er. A coercivity versus anisotropy field and composition. The R 15Fe 77B 8 has been constructed from the observed dependence of the coercivity on both temperature and composition. The role of boundary phases is discussed by comparing R 15Fe 77B 8 with SmCo 5 magnets.