In recent years, trans-1,3,3,3-tetrafluoropropene (R1234ze(E)) was proposed as a possible replacement for hydrofluorocarbons. In this work, the vapor-liquid phase equilibrium of R1234ze(E) with three imidazolium ionic liquids (ILs) were measured from (283.15 to 343.15) K based on the isochoric method. The ILs include 1-ethyl-3-methylimidazolium tetrafluoroborate ([Emim][BF4]), 1-hexyl-3-methylimidazolium tetrafluoroborate ([Hmim][BF4]), and 1-octyl-3-methylimidazolium tetrafluoroborate ([Omim][BF4]). The experimental results were correlated using the nonrandom two-liquid activity coefficients model. The deviations between experimental data and calculated values for pressure were 1.77%, 2.07%, and 2.32% for R1234ze(E) + [Emim][BF4], + [Hmim][BF4], and + [Omim]-[BF4] systems, respectively.