An optimised thermodynamic description of the Fe-B system is presented, based on the experimental thermochemical and phase diagram data using a least-square method. The model parameters for liquid, compound phases and solid solution phases near the Fe-rich side are obtained in that way. The solubility of Fe in B could not be modelled due to the lack of sufficient data. SGTE recommended expressions for the Gibbs energies of the pure elements have been used. The calculated phase diagram and thermochemical properties show good agreement with the experimental data.