A series of betaine-based salts containing quaternary ammonium ion and carboxylic acid group were synthesized by direct protonation of anhydrous betaine using different Bronsted acids. The catalytic activity of these salts for the synthesis of cyclic carbonates via cycloaddition reaction of CO, with epoxides was studied. The effects of anions of the salts, reaction temperature, pressure, reaction time, and the amount of catalyst used on the reaction were studied. It was demonstrated that the carboxylic acid group in the catalyst had synergetic effect with halide anion, and high yield of cyclic carbonates and excellent selectivity could be achieved at optimized condition. (C) 2008 Elsevier B.V. All rights reserved.