Conventional heat transfer fluid Therm500 has had its thermal conductivity improved with the use of BaO nanoparticles. Different concentrations of BaO:Therm500 nanofluids (from 0.001 to 0.006 g) are generated and characterised across a temperature range of 300 K, 303 K, 313 K, and 323 K. Studies using FT-IR spectroscopy on BaO:Therm500 nanofluids showed that there was no particle-fluid interaction. According to research on heat conductivity, this improvement may have occurred because of a combination of factors. As the temperature rises, the viscosity of the BaO:Therm500 nanofluids lowers, leading to an increase in the Brownian motion of nanoparticles and set convection-like effects, which in turn leads to improved thermal conductivity. Then, acoustic properties of Barium Oxide:Therm500 nanofluids are reported at four distinct temperatures, such as 300K, 303K, 313K, and 323K. For six different molar concentrations (0.001g, 0.002g, 0.003g, 0.004g, 0.005g, and 0.006g) of BaO nanofluids, density, refractive index and ultrasonic velocity values are measured and the acoustical parameters such as adiabatic compressibility (β), intermolecular free length (Lf), specific acoustic impedance (Z), Rao’s constant (R), molar compressibility (W), viscous relaxation time (τ), free volume (Vf), Gibbs free energy(ΔG) and internal pressure (πi) are calculated. Acoustical characteristics are used to investigate molecular interactions in nanofluid systems. The non-linearity of ultrasonic velocity with particle concentration has been observed due to weak particle – fluid interaction.