The Li2O-B2O3 quasi-binary system is assessed. A two-sublattice ionic solution model, (Li1+)(P)(O2-, BO33-, B4O72-, B3O4.5)(Q), is adopted to describe the liquid phase, All solid phases are treated as stoichiometric compounds. A set of parameters consistent with most of the available experimental data on phase diagram and thermodynamic properties is obtained by using the CALPHAD technique.