The effect of a salt on the kinetics of transfer of acetic acid at a free liquid/liquid boundary has been studied using the rotating membrane cell technique. LiCl, NaCl or KCl, at concentrations between 0 and 8 mol L-1, have been added to the aqueous phase. The organic phase was composed of a pure liquid: isopropylmyristate (isopropyltetradecanate). This type of system is interesting because it leads to a "simple" interfacial transfer process, consisting only of a change of solvation. The kinetic rate of transfer has been measured as a function of the salt concentration. The activity coefficient of the acetic acid in the aqueous phase containing salt has been determined experimentally by solvent partitioning. In contradiction with an often-made assumption, it has been found that this quantity is not sufficient for describing the effect of a salt on the kinetics of transfer of acetic acid. Specific effects occurring at the interface are expected to play an important role.