The vapor pressures for binary systems containing the ionic liquid (IL) 1-ethyl-3-methylimidazoliun tetrafluoroborate ([EMIM][BF4]) and a solute were measured with a modified equilibrium still, and the solutes investigated were benzene, toluene, thiophene, and water. The results indicate that the IL [EMIM][BF4] produces an obvious effect on the vapor pressures of binary systems, and the vapor pressures increase with the temperature. The vapor pressures of binary mixtures (i.e., [EMIM] [BEJ + benzene, [EMIM] [BF4] + thiophene, and [EMIM] [BF4] + toluene) first increase with the increase of mole fraction of the solute, and then almost keep stable. However, the vapor pressures of the mixture of water and [EMIM] [BF4] increase linearly with the increase of mole fraction of water. The vapor pressure experimental data for the binary systems were compared with the predicted values by the conductor-like screening model for real solvents (COSMO-RS) model. The results demonstrate that the COSMO-RS model gives quantitative prediction for the vapor pressure of the [EMIM][BF4] water system, but only qualitative prediction for other systems investigated in this work.