Ultrasonic absorption measurements have been made in aqueous acetic solutions at 15 to 85 MHz using pulse‐echo and pulse send‐receive techniques. A weighted nonlinear regression method has been developed for the computation of the relaxation parameters. A single relaxation has been found with a relaxation frequency at 13.2 MHz in 0.1Macetic acid and 66.1 MHz in 1.0Macetic acid at 25°C. These values and the maximum excess relaxational absorption per wavelength are in good agreement with the values calculated from equilibrium and kinetic parameters for the ionization of acetic acid as determined by non‐acoustical techniques (density, conductance, electrode kinetics, and Wien effect II dispersion). The rate constants and reaction volume change of the ionization‐association process, calculated from the ultrasonic absorption measurements in acetic acid, arekdissoc = 7.8 × 105 sec−1, kassoc = 4.4 × 1010 M−1 sec−1, andΔVdissoc = −11.2 cm3/moleat 25°C.