Abstract The enthalpies of solution of the hydrated lithium borates Li2B4O7·3H2O and LiB5O8·5H2O in approximately 1 mol·dm−3aqueous hydrochloric acid, as well as the enthalpies of solution of H3BO3in HCl(aq) and of LiCl·H2O in aqueous (hydrochloric acid+boric acid) were determined. With the incorporation of the standard molar enthalpies of formation ΔfHm0of LiCl·H2O(s), H3BO3(s), and H2O(l), the standard molar enthalpies of formation of these hydrated borates were obtained. An approach to correlate ΔfHm0of hydrated borates with ΔfHm0of corresponding cations in aqueous solution and ΔfHm0(H2O, l) was suggested from the point of view of structures.