This paper describes a chemical model that calculates solute and solvent activities and solid-liquid equilibria in the Li-H-Na-K-Cl-OH-H<sub>2</sub>O system from dilute to high solution concentration within the 0 to 250 °C temperature range. The model coherently extends to Li the temperature-variable H-Na-K-OH-Cl-H<sub>2</sub>O model of Christov and Møller (2004b, p. 1309). The solubility modeling approach based on Pitzer9s (1973, p. 268) specific interaction equations is used. All binary (LiCl-H<sub>2</sub>O and LiOH-H<sub>2</sub>O) and ternary (LiCl-HCl-H<sub>2</sub>O, LiCl-NaCl-H<sub>2</sub>O, LiCl-KCl-H<sub>2</sub>O, LiOH-NaOH-H<sub>2</sub>O, LiOH-KOH-H<sub>2</sub>O, and LiOH-LiCl-H<sub>2</sub>O) lithium subsystems are included in the model parameterization. The model for the LiCl-H<sub>2</sub>O system is parameterized using two different approaches: (1) with 4 ion interaction binary parameters (β<sup>(0)</sup>, β<sup>(1)</sup>, β<sup>(2)</sup>, and C<sup>ϕ</sup>), and (2) with 3 ion interaction binary parameters (β<sup>(0)</sup>, β<sup>(1)</sup>, and C<sup>ϕ</sup>) and including neutral aqueous LiCl<sup>0</sup>(aq) species. Approach (2) provides a better fit of activity data in unsaturated binary solutions and accurately predicts solid solubilities up to 40 mol.kg<sup>−1</sup> and up to 250 °C. Therefore, this approach was used to parameterize lithium chloride mixed systems. Temperature functions for the thermodynamic solubility product (as log K<sup>o</sup><sub>sp</sub>) of 5 simple lithium salts (LiCl.2H<sub>2</sub>O(cr), LiCl. H<sub>2</sub>O(cr), LiCl(cr), LiOH. H<sub>2</sub>O(cr), and LiOH(cr)) are determined. The log K<sup>o</sup><sub>sp</sub> values of 3 double lithium basic salts precipitating in the LiOH-LiCl-H<sub>2</sub>O system at 50 °C (3LiOH.LiCl(cr), LiOH.LiCl(cr), and LiOH.3LiCl(cr)) are also estimated using solubility data.