Vapor pressures were measured for acetonitrile + 1-butyl-3-methylimidazolium chloride ([C4mim][Cl]), + 1-butyl-3-methylimidazolium tetrafluoroborate ([C(4)mim][BF4]) and + 1-hexyl-3-methylimidazolium chloride ([C(6)mim][Cl]) at temperatures of 313 to 353 K by a quasi-staticmethod. The experimental data for the binary systems were correlated by the non-random two liquid (NRTL) equation with an average absolute relative deviation (AARD) of within 1.84%. The results indicate that the three ionic liquids (ILs) can result in a negative deviation from the Raoult's law for the binary solutions containing acetonitrile, and the affinity between ILs and acetonitrile molecules follows the order [C4mim][BF4] + acetonitrile > [C(4)mim][Cl] + acetonitrile > [C(6)mim][Cl] + acetonitrile. (C) 2014 The Chemical Industry and Engineering Society of China, and Chemical Industry Press. All rights reserved.