The enthalpy of solution of teepleite, Na2B(OH)(4)Cl, in approximately 1 mol dm(-3) aqueous hydrochloric acid was determined. Together with the previously determined enthalpies of solution of H3BO3 in approximately 1 mol dm(-3) HCl(aq), and of NaCl in aqueous (hydrochloric acid + boric acid), the standard molar enthalpy of formation of -2007.98 +/- 0. 84 J K-1 mol(-1) for Na2B(OH)(4)Cl was obtained from the standard molar enthalpies of formation NaCl(s), H3BO3(s), and H2O(l). The standard molar entropy of formation of -700.59 J K-1 mol(-1) and standard molar entropy of 190.62 J K-1 mol(-1) for Na2B(OH)(4)Cl were calculated from the thermodynamic relations. The group contribution method by Li is applicable to teepleite.