The solubility and stability of biomolecules may be influenced by the addition of cosolvents. Ionic liquids (ILs) have emerged as novel cosolvents for widespread applications in biotechnology and industrial processes. In the present study, we report the solubilities and apparent transfer free energy (Delta G(tr)') values for zwitterions containing glycine peptides (GPs) such as glycine (Gly), diglycine (Gly(2)), triglycine (Gly(3)), tetraglycine (Gly(4)), and cyclicglycylglycine (c(GG)) from water to aqueous solutions of imidazolium-based ILs at 25 degrees C and atmospheric pressure. ILs used here have different anions such as chloride (Cl-), bromide(Br-), hydrogen sulfate (HSO4-), acetate (CH3COO-), and thiocyanate (SCN-) and a common 1-butyl-3-methylimidazolium cation [Bmim]+. The Delta G(tr)' values of GPs from water to aqueous IL solutions have been obtained from the solubilities, which are determined from density (rho) measurements as a function of IL concentration at 25 degrees C. Further, we have calculated the salting constant (k) from the Setschenow equation, and the values have been analyzed with salting-out/salting-in effects. The experimental Delta G(tr)' data allowed the calculation of the transfer free energy contributions (Delta G(tr)')of the peptide backbone unit (-CH2C=ONH-) from water to aqueous ILs. The effects of anions of ILs on GPs have been analyzed through solubilities, stabilities, and Delta G(tr)' values to obtain a usual understanding of the Hofmeister series. The results are discussed in terms of solute-solute and solute-solvent interactions in the aqueous IL solution.