The stability constants for sulfate, chloride and hydroxide ions with cerium (III) in the solution at ionic strength of 0.67 have been determined by cation exchange method, the values ofΒ1andΒ2for sulfate complexes of cerium being 40±13 and 453±140, respectively and those for chloride complexes being 1.28±0.23 and 0.56±0.076, respectively. The values ofΒ1,Β2andΒ3for hydroxide complexes of cerium were (4.5±0.9)×107, (3.3±0.7)×1014and (1.8±0.7)×1023