The hydrolysis of Zr(IV) compounds was investigated using the horizontal zone electromigration method and zirconium 95 as radioactive indicator. For this reason the ion mobility of Zr(IV) was measured detecting the γ-rays of zirconium 95 at 298 Kin dependence on pH and for the both concentrations of czr≲ 10−8M and czr= 4 · 10−3M. At the lower concentration of Zr ions the hydrolysis constants of Zr ions were determined for the mononuclear hydroxides(i = 1 … 4). At the higher concentration (czr= 4 · 10−3M) polynuclear cationic species are formed.