Values of cmf for the cell without liquid junction Pt, H-2 (101.325 kPa) \ Li2B4O7 (m(1)), LiCl (m(2))\ AgCl-Ag are reported at five temperatures from 278.15 to 318.15 K. The standard association constant of ionic pair Li+B(OH)(4)(-), K-a, is determined by a fitting with the cell results. The dependence of pK(a) on temperature Tis expressed in empirical equation. pK(a)=-131.6K/T-0.08996-1.856x10(-3)T/K. The other thermodynamic quantities of the association process are calculated and show that there truly exists ion pair Li+B(OH)(4)(-) and the driving force for the ion association reaction is association entropy.