The capture of SO2 by ionic liquids (ILs) has drawn much attention. In this work, a series of triethylenetetramine (lactate)n ([TETA]L-n) was synthesized and triethylenetetramine tetralactate ([TETA]L-4) was selected to prepare aqueous IL solutions to absorb SO2. It has been found that the aqueous IL solutions can absorb large amounts of SO2; the saturated mole ratio of SO2 to IL in the aqueous IL solution decreases with increasing temperature, and increases with increasing water content of the aqueous IL solution; the density and viscosity of the aqueous IL solution decreases with increasing temperature and water content, and the density and viscosity of aqueous IL solution after SO2 absorption is higher than that before SO2 absorption. The absorption of SO2 by the aqueous IL solution is reversible. Compared with other ILs, [TETA]L-4 has many advantages in application, including inexpensive synthetic materials, uncomplicated synthetic procedures, high SO2 capacity, and excellent reversibility.