Ionic liquids (ILs) are a class of chemicals comprising cations and anions whose properties can be controlled by modifying their chemical structure, which enables a wide range of applications. Among the attractive properties of ILs, dielectric permittivity provides important information related to material solvation and capacitor characteristics. Because there are several ILs and a need to understand the structural effect on their properties, prediction model(s) should be developed. For this, we employed the linear free-energy relationship (LFER) equation to predict the dielectric constant of ILs. In the modeling, we used in silico calculated molecular descriptors because the empirically LFER estimated descriptors were limited. The results revealed that the developed model could predict the dielectric constant with an R2 of 0.882. From the developed model, it was observed that the dielectric constant was more affected by the structure of cations compared to that of anions. In addition, the H-bonding acidity of the cation and basicity of the anion contributed to the dielectric property of ILs, and the dipolarity/polarizability of cations and anions was also important in the prediction. The predictive model is expected to be useful for designing IL structures considering the dielectric constant.