Hydrolysis of aluminum(III) ion in 3.0 M(Na)NO3medium was studied by emf method at 25° C. Data cover the range 1–78 mMAl(III) within the pH range of 2.0–4.5. At a definite pH, the extent of hydrolysis increases with increasing aluminium concentration, thereby indicating the presence of polynuclear hydrolysis products. The least squares treatment of the data indicates the formation of polynuclear hydrolytic complexesandWith the reactions written in the formthe stability constants obtained were log (β2,2 = −7.55 ± 0.21, log β2,4 = −16.41 ± 0.13, and log (β3,4 = −13.24 ± 0.08. Distribution curves indicate that the complexis predominant.Keywords: hydrolysis, aluminum(III) ion, hydrolytic complexes, aluminum(III) ion hydrolysis.