The ultrasonic velocity (U) and density ( ) have been measured in the mixtures of Lithium Hydroxide and Lithium Bromide in Polyethylene glycol (400) solution in different concentrations at 303 K. Ultrasonic velocity has been measured using single frequency interferometer at 2 MHz (Model F-81). From the experimental data, other related thermodynamic parameters, viz adiabatic compressibility, intermolecular free length, and acoustic impedance are calculated. The compressibility of a solvent is higher than that of a solution and it decreases with the increase in concentration of the solution. The abrupt variation of a velocity indicates the formation of complex. Variations of the acoustical parameters in the binary mixtures are studied. The graph between ultrasonic velocity and volume of lithium salts solution in the mixed solution shows some peaks at a particular concentration. The present investigation comprises of theoretical evaluation of acoustic non-linearity parameter, B/A using Hartmann relation, Ballou’s empirical relation. A comparative study of B/A values obtained from the aforementioned methods has been made. The results are discussed on the basis of intermolecular interactions present in the liquid mixtures. The nonlinear variation of velocity indicates the complex formation between the constituents of the mixture. The results have been discussed in terms of various interactions present in these mixtures.