Experimental evidence for the preferential solvation of phenol in a mixed solvent of acetonitrile and water has been obtained by mass spectrometric analysis of the clusters isolated from liquid droplets by the adiabatic expansion. The effect of temperature on the formation of phenol–hydrate clusters, (C₆H₅OH)(H₂O)_n : n= 1,2,3, …, showed that phenol molecules are solbated preferentially by acetonitrile molecules at x_w(water mole fraction) < 0.85, the phenol–hydrate clusters were hardly observed at temperatures lower than 50 °C but appeared at higher temperatures. On the contrary, at x_w 0.85, hydrate formation became preferable at lower temperatures. The observed temperature effect confirmed microscopically inhomogeneous clustering of the solvent and solute molecules in the mixtures. A. similar temperature effect was also observed in the emission spectra of 2-naphthol in the same mixtures.