Abstract The densities of aqueous solutions of glycine, l -serine, l -alanine, l -proline with the ionic liquid (IL), 1-phenylpiperazinium tetrafluoroborate ([Phpi][BF4]) at the IL concentrations of (0.025, 0.055 and 0.100) mol·kg−1 have been measured at the temperatures of (298.15, 303.15 and 308.15) K. On the basis of the experimental results, the apparent molar volume (VФ), standard partial molar volume (VФ0), transfer partial molar volume (ΔtrVΦ0) and hydration number (nH) have been calculated. The hydrophilic–hydrophilic, hydrophobic–hydrophilic and hydrophobic–hydrophobic interactions are involved in the studied systems of {[Phpi][BF4] + amino acids + H2O. These volumetric parameters can help to understand the mixing effects and other complex biological processes between amino acids and ionic liquid aqueous solution.