Density and ultrasonic velocity of poly(propylene glycol) in aqueous solutions of tri-potassium citrate have been measured at T = (288.15 to 313.15) K at atmospheric pressure. From these measurements, the excess specific volume, isentropic compressibility, and isentropic compressibility deviation values have been determined. It has been found that the excess specific volume and isentropic compressibility deviation are negative and decrease in magnitude as temperature or concentration of tri-potassium citrate increases.