Abstract: Polyethylene glycol (PEG), a low toxicity and stable water-soluble polymer compound, is widely used as the auxiliary material, solvent, additive and modifier. Its behavior in aqueous solution has been studied through spectroscopy, chromatograph, molecular simulation and many other experiments, but the study of structures and interactions in PEG/alcohol/water solution is scarce, which has important sigficance for the application of PEG. In this paper, the properties of a series of PEG/2-butoxyethanol (2BE)/water solutions were studied by measuring dynamic light scattering, resonance light scattering, density and heat capacity. The particle size distribution and resonance light scattering intensity of 2BE/H₂O and PEG/2BE/H₂O solutions determined by light scattering experiments showed that 2BE content affected the aggregation structures and interactions in solutions, and the addition of PEG molecules destroied and recombined the 2BE/H₂O association aggregates and the 2BE self-association aggregates, which increased the sizes of the aggregates. The apparent molar volume of infinite dilution (V_\varPhi ,\rmPEG^0), the interaction parameter (S_V) and the apparent molar heat capacity (C_Φ,PEG) for PEG chain in 2BE/H₂O mixed solvents were deduced from the data of density and heat capacity at 25 ℃. V_\varPhi ,\rmPEG^0 reached the minimum value at x_2BE=0.0242; S_V increased first, then decreased and finally increased again with the increase of x_2BE, and changed from the negative to the positive at x_2BE=0.0167, and had a positive maximum at x_2BE=0.0242; C_Φ,PEG decreased with the increase of x_2BE, but the decrease became not obvious when x_2BE>0.0167. The above characteristic changes of macroscopic thermodynamic variables were consistent with the structures and interactions in the solutions.