Ionic liquids (ILs) are potentially suitable compounds as replacements for organic solvents in chemical processes and play an important role in reducing the production of toxic compounds. In this work, the electrolyte Perturbed-Chain Statistical Associating Fluid Theory (ePC-SAFT) equation of state (EoS) was utilized to predict the second-order thermodynamic derivative properties including isothermal compressibility coefficient, thermal expansion coefficient, heat capacities, thermal pressure coefficient, isentropic compressibility coefficient, and speed of sound of imidazolium-based ionic liquids with [BE4](-), [Tf2N](-), and [PF6](-) anions. Two ionic dissociation models were considered. The first model assumes a complete dissociation of IL molecule into ions (full dissociation), while the second model considers partial dissociation of molecules into ions where molecules, anions, and cations coexist in the liquid phase. The first model is convenient when applying ePC-SAFT to ILs. The second model, however, is new within ePC-SAFT. The secondorder thermodynamic derivative properties of pure ILs were predicted with partially and fully ionic dissociation approaches and compared to available experimental data from the literature. The parameters of ePC-SAFT with the partial dissociation approach were estimated by fitting the experimental liquid density from the literature. The comparison of results from the two methods with experimental data showed that the predictions by the partial dissociation approach were more accurate than those by the full dissociation approach. The improved accuracy might be a result of better approximation of the real ionic liquid systems by the partial dissociation assumption.