The rate of hydrogen absorption in cathodically polarized zirconium was measured by using the differential etching method, in which the specimen covered with hydride was dissolved layer by layer from surface in hydrofluoric acid solution containing hydrogen peroxide, and the volume of liberated hydrogen was determined with a gas burette. Sigmoid in-depth hydrogen concentration profile was obtained with this technique and the results were ascertained both by the methods of the (d, n) reaction and the mass spectrometric measurement. Total amount of absorbed hydrogen and the thickness of hydride layer were estimated respectively by the integration of the profile and the determination of the profile front. In general tendency, the linear and the parabolic rate laws were held before and after the absorption reached at the level of 0.3 NTP cm³/cm² respectively. The existence of alkaline salt in the electrolyte stimulated the absorption, and abnormally high surface hydrogen content in the hydride layer was observed. Under the condition of galvanostatically cathodic polarization the maximum absorption was obtained at pH=7 in any kind of electrolyte. The mechanism of absorption process was discussed on the basis of the kinetic relations among the intial rate of absorption, the electrolytic current and the electrode potential.