The results of experimental measurements of the sound velocity in aqueous potassium hydroxide solutions are given. The region of anomalous temperature dependence of the sound velocity is determined. An equation is obtained for the sound velocity at atmospheric pressure as a function of temperature and composition. A second equation is obtained is valid for solutions with concentrations up to 60% at the temperatures 223-573 K and at pressures up to 60 MPa. The correlations for the density and the isobaric heat capacity of solutions at atmospheric pressure are presented also. The isochoric heat capacity data for the potassium hydroxide-water system are calculated.