Vapor pressure data were measured for nine binary systems containing water, ethanol, or methanol with one of three protonic ionic liquids (PILs), viz, mono-, di- and tri-ethanolammonium tetrafluoroborate ([HMEA][BF4], [HDEA][BF4]. and [HTEA][BF4]), at varying temperatures and PIL-contents using a quasi-static ebulliometer. The vapor pressure data were correlated by NRTL model with an overall average absolute relative deviation (AARD) of 0.0175. It is showed that the effect of PILs on the vapor pressure lowering of solvents follows the order of [HMEA][BF4] > [HDEA][BF4] > [HTEA][BF4], and the vapor pressure lowering degree follows the order of water > methanol > ethanol. Besides, the activity coefficients of solvent for binary system {solvent + PIL} at fixed PIL mole fraction of 0.10 were calculated using the regressed NRTL parameters. The results indicate that three PILs can give rise to a negative deviation from the Raoult's law for water and methanol and a positive deviation for ethanol to a varying degree, leading to the variation of relative volatility of a solvent. (C) 2011 Elsevier B.V. All rights reserved.