The sulphate - complexes of tetravalent cerium have been studied. Their stability and conditions of their formation solutions has been investigated . In addition the ease of hydrolysis of tetravalent cerium salts in sulphate solutions indicates a lower stability for the monosulphato tetravalent creium ion . The instability constants of the corresponding complexes were calculated from the results of spectrophotometric measurments . In dilute sulphate solutions of tetravalent cerium the complex cation [CeSO4]24- is predominant ; Knst = 2.6 x 10-3 .When the concentration is raised to 0.05 M mainly the neutral complex Ce(SO4)2 is formed ; Knst = 5.9 x 10-3 . In solutions containing an excess of sulphuric acid , cerium exists mainly as a complex anion.