We have studied the microscopic solvent structure of dimethyl sulfoxide-water mixtures and its influence on the solvation structure of solute from a clustering point of view, by means of a specially designed mass spectrometric system. It was observed that the propensity to the cluster formation is nonlinearly dependent on the solvent composition, exhibiting the existence of a critical value of mixing ratios where drastic changes in the microscopic solvent structure occur. It was also demonstrated that in such a solvent mixture the solvation structure of solutes such as 2-butanol, cyclopentanol, cyclohexanol, and phenol is greatly related to the microscopic solvent structures, implying that solute species interact with already established solvent clusters, rather than with individual solvent molecules.