In this study, the effect of Tb inward diffusion on the magnetic properties of the Nd-Fe-B sintered magnets was studied. After sintering of the magnets, TbF₃ slurries were dip-coated on the surface of the samples, then heat-treatment was followed for TbF₃ diffusion. The element distribution in the magnets and the diffusion profiles of Tb ions were analyzed by an EPMA (electron probe micro-analyzer). Prolonged heat treatment resulted in a deeper diffusion length of Tb ions. Coercivity of the 1^st heat-treated sample showed 21.86 kOe, while that of the 1^st, 2^nd heat-treated and annealed sample revealed 34 kOe.