The hydration of two-dimensional (2D) particles in aqueous solutions plays an important role in many scientific and technological fields. In this work, a novel method for the determination of the thickness of hydration shell on nanosheets in water has been presented, which was realized through the measurements of the viscosity of aqueous nanosheet dispersion as the function of solid volume concentration and the thickness and size of the nano sheets with atomic force microscope. The principle of the method was based on the viscosity theory of the dispersions of solid nanosheets. This method was applied to montmorillonite nanosheets, showing that the thickness of the hydration shell on the nanosheets was of 1.63 nm. This value of the thickness was verified by molecular dynamics simulation. (C) 2016 Elsevier B.V. All rights reserved.