We propose a theory of viscosity derived using the perturbation expansion of microscopic equations describing solvent particle dynamics to study the solvation effects of a two-component solvent in the vicinity of a large solute. The microscopic theory is expanded in powers of the solvent???solute size ratio. Considering the density distribution of the solvent particles around the solute particle, we obtain hydrodynamic equations with the boundary conditions on the solute surface. Solute???solvent radial distribution functions give the boundary condition. The perturbation theory allows us to compare the viscosity of a pure binary solvent with that of a solution including solute particles. On the basis of the theory, we determine the effects of the solute-surface mass density of solvent particles on viscosity using model radial distribution functions. We also examine some realistic distribution functions on the basis of the integral equation theory.