Abstract: Density functional theory (DFT) calculations were carried out to study the structures,intermolecular interactions,and basicity of ionic liquids formed by six amino acid-based anions and the imidazolium cations with different side chain lengths.Five locally stable conformers of the ion pairs were located,and two kinds of hydrogen bonds were obtained by optimization.The atoms in molecules (AIM),noncovalent interaction (NCI),and natural bond orbital (NBO) analysis were undertaken.Hydrogen bonds between the carbonyl O in the anions and H(C2) are much stronger in strength and have some covalent character.Finally,the basicity of these ionic liquids was analyzed at the microscopic level,using the surface electrostatic potential (V_s,min) and the lowest surface average local ionization energy (I_s,min).The basicity of these ionic liquids could be enhanced with the introduction of an amine or hydroxyl group into the anion.