Functionalized ionic liquids (ILs) have been demonstrated to absorb SO2 from mixed gases or simulated flue gases efficiently. However, after absorbing a large amount Of SO2, the viscosity of the ILs increases greatly, which might limit their eventual applications in large-scale desulfurization from mixed gases or flue gases. In this work, the effect of the presence of water in a simulated flue gas on the absorption Of SO2 by a functionalized ionic liquid, 1,1,3,3-tetramethylguanidinium lactate, has been studied at different temperatures. It is found that the presence of water in the simulated flue gas can decrease the viscosity of the IL greatly, and it has no effect on the absorptivity Of SO2 from the flue gas. The densities of the IL absorbing SO2 from the flue gas With or without water are also studied. They increase with the increase of the amount Of SO2 absorbed from the flue gas in both cases.