An apparatus used to measure vapor pressure of organic solvents was set LIP. and vapor pressure of mixture of ionic liquids ([BMIM][PF6] and [BMIM][BF4]) and aromatic compounds (benzene and thiophene), with mole fraction of organic solute from 0.1 to 0.75 was measured by using saturation vapor pressure method at temperature from 303 K to 343 K. Then NRTL equation was used to correlate the experimental data. The overall average relative deviation of activity coefficients for the whole system is 2.30%, which indicates that NTRL equation can be utilized to correlate vapor pressure of binary systems containing ionic liquids. The results show that ionic liquids can depress the volatility of aromatic compounds. (C) 2008 Elsevier B.V. All rights reserved.