The enthalpies of solution of two hydrated lithium monoborates in approximately 1 mol dm(-3) aqueous hydrochloric acid were determined. From these results and the enthalpies of solution of H3BO3 in approximately 1 mol dm(-3) HCl(aq), and of LiCl.H2O in aqueous(hydrochloric acid + boric acid),combining with the standard molar enthalpies of formation of LiCl.H2O(s), H3BO3(s) and H2O(1), the standard molar enthalpies of formation of -1627.46 +/- 0.90 and -3397.00 +/- 0.94 kJ mol(-1) for LiBO2.2H(2)O and LiBO2.8H(2)O were obtained. The standard molar entropies of formation of LiBO2.2H(2)O and LiBO2.8H(2)O were calculated from the thermodynamic relation with the standard molar Gibbs free energy of formation of LiBO2.2H(2)O and LiBO2.8H(2)O computed from a group contribution method. (C) 2004 Published by Elsevier B.V.