The interaction between poly(ethylene glycol)-400 (PEG-400) and tetraethylammonium bromide (Et 4 NBr) has been investigated through density, ultrasonic velocity, viscosity, and 1 H NMR measurements at 303.15 K. The concentration of PEG-400 has been varied in the aqueous media containing a fixed amount of Et 4 NBr (1–20 wt.%). The apparent and transfer properties including the apparent molal volume V ϕ,s , isentropic compressibility K ϕ,s , solvation number n s , and reduced viscosity η red , respectively, have been deduced from the experimental data. The infinite dilution values of V ϕ,s and K ϕ,s of the solvated species are also estimated by extrapolation towards infinite dilution. The ultrasonic velocity shows the apparent breakdown in variation with the polymer concentration. The viscosity measurement enables to observe the concomitant reorganization of the solute species. The stoichiometry of the solvated species has been investigated by means of 1 H NMR analysis.