Vapor–liquid equilibrium data of binary mixtures containing imidazolium ionic liquids were correlated using the UNIQUAC activity coefficient model optimized with a particle swarm algorithm. Twenty eight binary systems taken from literature were selected for this study, and the new optimization algorithm was used to determine the binary interaction parameters of each system. The results given by the model have been compared with experimental data, and show that the optimized UNIQUAC model is a good model to correlate and predict the vapor–liquid equilibrium for this type of systems. • PSO was used for the thermodynamic modeling of the vapor–liquid phase of 28 mixtures containing ionic liquids. • Binary interaction parameters of the UNIQUAC activity coefficient model were optimized. • The proposed model is reliable enough to estimate the vapor–liquid phase equilibrium with an average deviation of 3%.