An ionic liquid system of [Bmim]X/[Bmim]OH (X = Cl, BF4, and PF6,) was developed for the hydrolysis of ethylene carbonate to ethylene glycol. The important parameters, such as the variety of ionic liquids, molar ratio of [Bmim]X to [Bmim]OH, amount of ionic liquid, molar ratio of water to ethylene carbonate, reaction temperature, pressure and reaction time, were investigated systematically. Excellent yield (>93%) and high selectivity (99.5%) of ethylene glycol were achieved. Under the optimum reaction conditions, the ionic liquid system could be reused at least five times and the selectivity of ethylene glycol remained higher than 99.5%.