Ester-functionalized anionic surface-active ionic liquids (SAILs), 3-methyl-1-(ethoxycarbonylmethyl)imidazolium dodecylsulfate ([C(1)COOC(2)C(1)im][C(12)SO(4)]) and 3-methyl-1-(ethoxycarbonylmethyl)pyrrolidinium dodecylsulfate ([C(1)COOC(2)C(1)Py][C(12)SO(4)]), were synthesized. The tensiometric profiles demonstrate that, in pure water, the studied SAILs exhibit higher surface activity than the traditional anionic surfactant, sodium dodecyl sulfate (SDS), and cationic SAILs, 1-dodecyl-3-methylimidazolium bromide ([C(12)mim]Br) and N-dodecyl-N-methylpyrrolidimium bromide (C(12)MPB), with the same hydrocarbon chain length. The interaction between bovine serum albumin (BSA) and the anionic SAILs in pH 7.4 buffer solution was systematically investigated by various techniques. The results show that the cationic ring has a slight effect on the BSA-SAIL interaction. The binding isotherms of BSA with the SAILs display four characteristic regions with increasing SAIL concentration. The unfolding of BSA occurs in the third region. Fluorescence spectroscopy indicates that the studied SAILs cause the exposure of tryptophan residues to a hydrophobic environment, and [C(1)COOC(2)C(1)im][C(12)SO(4)] can more effectively reduce the fluorescence intensity of BSA at low SAIL concentrations than [C(1)COOC(2)C(1)Py][C(12)SO(4)]. Circular dichroism spectroscopy evidences that the denaturation extent of BSA induced by [C(1)COOC(2)C(1)im][C(12)SO(4)] is higher than that of [C(1)COOC(2)C(1)Py][C(12)SO(4)].