In the separation processes of amino acids, zwitterionic species are prevented from being exchanged because of the spatial proximity of two opposite charges on the molecule. There would be a high chemicals cost due to the need to change the solution pH. It is therefore desirable to develop a novel recovery technology for amino acids in the middle pH range. A series of extraction equilibrium experiments for L-phenylalanine (L-phe) with di(2-ethylhexyl) phosphoric acid (D2EHPA) dissolved in n-octane was carried our. The effects of L-phe concentration, D2EHPA concentration, and pH on the distribution ratio were discussed in detail. The infrared spectrogram of the organic-phase-loaded solute illustrated that the pH condition had little effect on the structure of the complex. There are proton-transfer and ion-exchange reactions in the extraction. One L-phe molecule is extracted by forming a complex with two dimeric D2EHPA molecules. An expression of the equilibrium distribution was proposed.