A pure hydrated double strontium borates, K2Sr[B4O5(OH)(4)](2)-10H(2)O, has been synthesized and characterized by XRD, FT-IR, DTA-TG and chemical analysis. The enthalpies of solution of K2Sr[B4O5(OH)(4)](2)(.)10H(2)O in 1 mol dm(-3) HCl(aq) and KCl(s) in mixed solvent [1 mol dm(-3) HCl + Sr(OH)(2)(.)8H(2)O + H3BO3](aq) were determined. With the incorporation of the previously determined enthalpies of solution of Sr(OH)(2.8)H-2 O(S) in [1 mot dm(-3) HCl + H3BO3](aq), H3BO3(S) in 1 mol dm(-3) HCl(aq) and the standard molar enthalpies of formation of HCl(aq), H2O(1), Sr(OH)(2)(.)8H(2)O(s), H3BO3(s) and KCl(s), the standard molar enthalpy of formation of K2Sr[B4O5(OH)(4)](2) - 10H(2)O was found to be -(10882.0 +/- 6.5) kJ mol(-1). Thermodynamic properties of the compound were also estimated by a group contribution method. The standard molar free energy of formation (Delta(f)G(m)degrees) was estimated to be -9690.80 U mot-'. From these values, the standard molar entropy of formation (Delta S-f(m)degrees) was estimated to be -3995.3 J mol(-1) K-1. The standard molar entropy (S-m degrees) was estimated to be 933.8 J mol(-1) K-1. (c) 2007 Elsevier B.V. All rights reserved.