Abstract In this study, binary LLE data at 313.2, 333.2, and 353.2 K, binary VLE data in the pressure range of 3–30 kPa and ternary VLE data at 5, 10, and 15 kPa have been determined for the system ethylbenzene + styrene + [3-mebupy][B(CN) 4]. The IL [3-mebupy][B(CN) 4] can increase the relative volatility of the ethylbenzene/styrene mixture from 1.4 without solvent up to 2.2 and is therefore a promising solvent. The binary and ternary VLE data were regressed separately with the NRTL model. The correlation statistics demonstrated that the NRTL model can describe the experimental data adequately. It was not possible to get a proper description of the ternary VLE data with the NRTL parameters determined solely from the binary systems.