The mixtures of ionic liquid (IL) tetrabutylphosphonium trifluoroacetate (［P₄₄₄₄］CF₃COO) or tributyloctylphosphonium bromide (［P₄₄₄₈］Br) with water showed a lower critical eutectic temperature (LCST)-type phase behavior.Biomolecules could be extracted with the LCST-type systems by controlling the temperature.The effects of amino acid (AA) on the phase transition temperature of [P₄₄₄₄］CF₃COO-water and ［P₄₄₄₈］Br-water mixtures were investigated.Moreover,the distribution characteristics of AAs in the two phases were analyzed.Results showed that the addition of lysine,alanine,glycine,arginine and proline with the mass fraction of 2%-10% could enhance the phase formation ability of the mixtures.In addition,the IL-rich phase transferred from the lower phase to the upper phase with the increase amount of AAs and temperature.Herein,AAs were not only the target extractive,but also could assist the LCST-type ionic liquid-water mixtures to regulate phase equilibrium in the extraction of other biomolecules.This study can provide a basic data for the design of selective extraction of biomolecules by liquid-liquid systems containing ILs.