A pure barium borate of BaB8O11(OH)(4)center dot 3H(2)O has been synthesized and characterized by XRD, FT-IR, TGA, and chemical analysis. The molar enthalpies of solution of BaB8O11(OH)(4)center dot 3H(2)O in 1 mol dm(-3)HCl(aq), and Ba(OH)(2)center dot 8H(2)O in the mixture solvent of {2.00 cm(3) of 1 mol.dm(-3 )HCl + H3BO3 (aq)} were measured by microcalorimeter at T= 298.15 K, respectively. With the use of previously determined enthalpy of solution of H3BO3 (s) in 1 mol.dm(-3) HCl(aq), and the standard molar enthalpies of formation for Ba(OH)(2)center dot 8H(2)O(s),H3BO3 (s), and H2O(1), the standard molar enthalpy of formation of -(7500.6 +/- 6.5) kJ.mol (-1) at T= 298.15 K was obtained based on an appropriate thermochemical cycle. Moreover, the molar enthalpy of formation of -6091.7 kJ mol(-1) for [B8O11(OH)(4)](2) was estimated by a group contribution method, which was used to predict the Delta H-f(m)o of a series of alkaline-earth metal borates for MB8O11(OH)(4)(M = Ca, Sr, Ba). (C) 2019 Elsevier Ltd.