Some novel Brønsted acidic ionic liquids (TSILs) that bear an alkane sulfonic acid group in an acyclic trialkanylammonium cation were synthesized and their uses as dual solvent−catalysts for Fischer esterification reactions of acetic acid, metacetonic acid, and benzoic acid with ethanol, butanol, and benzyl alcohol were investigated. The reactions were completed smoothly at room temperature to 110 °C for 1.5−3.0 h with good yields of 88−95%. The results indicate that catalytic activity depends on anion acidity and the solubility of the starting material in TSILs. The increasing of the anion's acidity improves the catalytic activity of the TSILs. Furthermore, the produced esters could be separated by decantation after the reaction and the TSILs could be reused without noticeably decreasing the catalytic activity.