Ionic liquids consisting of triethylamine hydrochloride and anhydrous aluminium chloride (Et3NHCl-AICl(3)) were found to work well as Lewis acid catalysts in the synthesis of bisphenol A by condensation of phenol with acetone. Under the optimum conditions (a molar ratio of 8:1 of phenol to acetone, 10.7 mmol Et3NHCl-AlCl3, N = 0.6 per 10 mmol acetone, 0.2 mmol mercaptan per 10 mmol acetone, 60degreesC for 4 h in 25 mL toluene) the selectivity and the yield can reach 94.70 and 85.05%, respectively.