Recently, ionic liquids (ILs) were widely used to form aqueous biphasic systems (ABSs). In this study, a systematic investigation involving various ILs was studied to provide more information on forming IL-ABSs. For this purpose, based on the IL cations, n-butylpyridinium trifluoromethanesulfonate, n-butylpyridinium tetrafluoroborate, and n-butylpyridinium nitrate, the influence of anions of the IL on forming ABSs was evaluated. The cation effect between 1-n-butyl-4-methylpyridinium tetrafluoroborate and n-butylpyridinium tetrafluoroborate was discussed. Besides, bimodal curves data of all the studied ABSs were measured and presented. The binodal curves were then correlated by the Merchuk equation with values of R-2 > 0.9966, which is widely used to fit the binodal curves. Moreover, the influence of temperature on ABSs was studied for [4-MBP]BF4 + (NH4)(2)SO4 + water. The two-phase region in the diagram is found to increase as the temperature decreases.