Owing to some desirable properties, ionic liquids (ILs) have attracted increasing interests and applications in many domains. Unfortunately, however, they generally have much higher viscosities than conventional molecular solvents, which result to some problems of handling or transferring in chemical processing. ILs with lower viscosity are desired. Therefore, understanding the relationship between micro-structure and macro-viscosity along with a comprehensive viscosity data is important for the synthesis and rational design of ILs with low viscosity. In this work, a comprehensive collection of viscosity data covering the period of 1983-2009 is conducted on the pure imidazolium-based ILs, and quantitative structure-property relationship (QSPR) study is performed for four selected data sets. The four correlations are obtained with R-2 > 0.93, and quantum-chemical descriptors gave significant contributions. The cation-anion electrostatic interaction has the significant effects on the viscosity of imidazolium-based ILs, while other interactions (e.g., interionic hydrogen-bond, van der Waals) or micro-characteristics (e.g., molecular orbital, electronic population, dipole moment, volume, shape, branching degree, symmetry) also give some effects. (C) 2010 Elsevier B.V. All rights reserved.