Polypropylene glycol or polypropylene oxide is the polymer of propylene glycol. Chemically it is a polyether. The term polypropylene glycol or PPG is reserved for low to medium range molar mass polymer when the nature of the end-group, which is usually a hydroxyl group, still matters. PPG is used as a rheology modifier, surfactant, wetting agent, calibrant in mass spectrometry. In the present study, we have tried to compute the ultrasonic velocity and refractive index of binary liquid mixture of Polypropylene glycol (Molar mass : 1000) (PPG 1000) with benzene at different molar concentrations (0, 0.0215, 0.0554, 0.0809, 0.1166, 0.2603 and 1), at different temperatures (303 K, 308 K, 313 K __ampersandsign 318 K). The experimental ultrasound velocities are compared with various theoretical values like Nomotto’s relation, Impedance relation and Junjie’s relation. The experimental refractive index values are compared with various theoretical methods like Arago-Biot relation, Gladstone-Dale equation and Eyring-John equation. The most reliable method that matches with experimental method is identified by calculating average percentage error (APE) and discussions are made in the light of molecular interactions occurring in the binary liquid systems.