Based on electrolyte non-random two-liquid (e-NRTL) equation, a new activity coefficient model is proposed for the solution of ionic liquid + molecular solute. In the new model, the sizes of particles have been taken into consideration by introducing volume elements into the new model. For easier application, the Pitzer-Debye-Flfickel expression is cancelled in the new model, because ionic liquids work as solvents more frequently. To simplify the model, the assumptions (local electroneutrality and like-ion repulsion) have been made, which were adopted in Chen's e-NRTL model. As a result, the new model only needs 5 parameters like NRTL equation. Moreover, the new model can predict accurate results with fewer experiment data in comparison with NRTL for both totally miscible and partially miscible solutions, which has been proven with 19 kinds of solution. (C) 2019 Elsevier B.V. All rights reserved.