The modified UNIFAC-VISCO model was applied to evaluate the viscosity of (ionic liquid + molecular solvent) mixtures as the function of the composition and temperature at atmospheric pressure. The values of interaction parameters between ionic groups, were collected from our previous paper (Zhao et al. J. Chem. Eng. Data 61 (2016) 3908-3921), while the parameters between the common organic groups, were taken from Chevalier et al. (Chem. Eng. Sci. 49 (1994) 1799–1806). Another 376 unknown interaction parameters ( and ) were calculated by regression of 3365 experimental binary viscosity data for 119 different binary systems as a function of temperature and component composition. Then, this model was assessed through the evaluation of 781 viscosity data points for 24 different binary systems not originally included in the correlation set. The relative absolute average deviation (RAAD%) of the correlation and evaluation for the viscosity of the investigated binary mixtures is close to 5.0% and 7.7%, respectively, which proves that the UNIFAC-VISCO based method proposed in this work is reliable for the estimation of the viscosity of ionic liquid-based binary mixtures.