Vapor-liquid equilibrium(VLE) data were measured for ternary system water+ethanol+1-butyl-3methylimidazolium acetate([bmim

]

[OAc

]

)

in a relatively wide range of ionic liquid(IL) mass fractions up to 0.8.Six sets of complete

T-x-y

data were obtained

in which the mole fraction of ethanol on IL-free basis was fixed separately at 0.1

0.2

0.4

0.6

0.8

and approximate 0.98.The non-random-two-liquid(NRTL) and electrolyte non-random-two-liquid(eNRTL) equations were used for correlation

showing similar deviations.The ternary VLE was also modeled with the correlation from two data sets

with the mole fractions of ethanol on IL-free basis being 0.1 and approximate 0.98.The VLE data were also reproduced satisfactorily.With the eNRTL model

the root-mean-square deviation for temperature is 0.79 K and that for vapor-phase mole fraction is 0.0094.The calculations are in good agreement with experimental data.The effect of the IL on the VLE behavior of the volatile components is also illustrated.