Values of e.m.f, for the cell without liquid junction:Pt H-2 (p = 101.325kPa)\K2B4O7(m(1))LiCl(m(2))\AgCl Agare reported at seven constant ionic strengths from 0.07 to 2.0 mol.kg(-1) at five temperatures from 278.15 K to 318.15 K. The standard association constant K-a of the ionic pair Li+B(OH)(4)(-), is determined by a fit with the cell results. The dependence of pK(a) on temperature T is expressed by the empirical equation : pK(a) = -149.8(K/T) + 0.09024 - 2.112.10(-3)(T/K). The other thermodynamic quantities of the association process were also calculated and show that the driving force for the ion association reaction is the association entropy.