A functional 2-ethyl-4-methylimidazole alanine ([Emim] [Ala]) ionic liquid was synthesized. Its density, viscosity, and surface tension were measured at the temperature range from 293.15 to 343.15 K at atmosphere pressure. The solubility of SO2 in pure [Emim] [Ala] ionic liquid and the binary mixture of [Emim] [Ala] and water was also investigated. The absorption desorption mechanism of SO2 was proposed on the basis of C-13 nuclear magnetic resonance and Fourier transform infrared spectroscopy. Results showed that SO2 was captured as ammonia sulfonic acid ester by pure [Emim] [Ala], while for the binary mixture of [Emim][Ala] and water, the final product of SO2 absorption is alanine and [Emim](+)[HSO3](-)/[Emim](2)(+)[SO3](2-).