An extensive investigation on the diffusion and precipitation of Sb implanted in Si has been carried out. The rapid epitaxial regrowth of the amorphous layer produced by the incident ions brings Sb atoms into a substitutional position up to a concentration threshold of about 3.5 × 1020cm−3. This high supersaturation (the solubility of Sb in Si is about 2 × 1019cm−3at 1000 °C) and the low value of the surface free energy facilitate the nucleation of precipitates, which form and grow in concomitance with the diffusion during the annealing. The kinetics of the precipitation has been investigated at 800, 900, and 1000 °C with isothermal treatments ranging between 3 min and 341 h. The experimental data have been compared with the results of a simulation program that takes into account the precipitation phenomena. Good agreement has been obtained for all the investigated experimental conditions both for total and carrier distributions. The model represents a significant improvement of the simulation of Sb diffusion in silicon; in fact, the more commonly used process codes are inadequate to correctly foresee the dopant distribution in supersaturated conditions.