The solubilities of 1,2,3-trimethylbenzene, 1,2,4-trimethylbenzene and 1,3,5-trimethylbenzene in mixed solvents of t-butyl alcohol (TBA) and water at 283.15, 288.15, 293.15 and 298.15 K have been determined by spectmphotometry. The mole fractions of TBA [x(TBA)] in the mixed solvent are0.000, 0.010, 0.020, 0.030, 0.040, 0.045, 0.050, 0.060, 0.080 and 0.1000. The Gibbs energies of hydrophobic interaction (HI) for the aggregating process of three methane molecules with one benene molecule in the mixed solvent are studied, and the effect of solvent structure and solute aggregating state on the strength of HI is discussed.