The aim of the present study was to Study the extraction of lactic acid with tributylphosphate (TBP) dissolved in a diluent (dodecane) over a broad range of acid concentrations and solvent compositions, to determine the apparent equilibrium constants and the number of reacting extractant molecules, and to elucidate the influence of different factors (preliminary washing of organic phase, change of phase volumes, pH at equilibrium, acid concentration) oil the extraction of the acid. It was found that the change of phase volumes after extraction should be taken into account For the calculation of different process parameters. The preliminary washing of the extractant does not significantly affect the overall distribution coefficients.