The present paper deals with the effect of di-and tri-n-octylamine (DOA and TOA) dissolved in non-polar diluents or the mixture of non-polar diluents and modifier on the extraction of L-lactic acid from aqueous solutions. The amount of lactic acid extracted to the organic phase at equilibrium is dependent on the initial concentration of lactic acid in the aqueous phase as well as on that of amine in the organic phase. The results confirmed that almost the entire portion of lactic acid can be effectively extracted when the DOA concentration exceeds the initial concentration of lactic acid in the aqueous phase, and that TOA has little ability for the extraction when it is dissolved in non-polar diluent. Adding a modifier (decanol) to a non-polar diluent is also demonstrated to be effective for improving the extraction ability of TOA. The influence of the equilibrium pH value on the distribution ratio of lactic acid can be reasonably characterized by modifying the conventional ion-pair extraction model.