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 1st heat-treated sample showed 21.86 kOe, while that of the 1st, 2nd heat-treated and annealed sample revealed 34 kOe.