Several water-stable Brønsted-acidic ionic liquids with an alkane sulfonic acid group were synthesized, and were characterized by nuclear magnetic resonance (NMR), infrared spectrum (IR), electrospray ionization mass spectrum (ESI-MS) and thermogravimetry (TG.). It was found that their structures were consistent with the designed one and all of their purities were more than 95%. These ionic liquids possess high thermal stability and wide liquid range, and their decomposition temperatures are higher than 300 degrees C by analyzing TG. In addition, they were found to have four kinds of ionic form, in which hydrogen ion can exist independently by analyzing ESI-MS. Moreover, the solubility of these ionic liquids was studied in some common solvents. All the ionic liquids are miscible with water and methanol, but are insoluble in ether, toluene and ethyl acetate.