Cadmium is a highly toxic metal actively migrating in the system water-suspended sediments-bottom sediments. The paper aims to study the Cd content in the water and bottom sediments of the Sea of Azov in 1991-2020 and to evaluate the process of sedimentation self-purification of waters. The data on Cd distribution showed that from 1991 to 2009 its concentration decreased slowly in the water of the open part of the sea and in Taganrog Bay with an increase in 2010-2016. Cd concentration in the Sea of Azov water did not exceed the maximum permissible concentration (10 μg/L) for marine waters of fisheries. Levels of Cd contamination in bottom sediments were assessed by comparison with the soil contamination criteria according to the Dutch List. The Cd content in the bottom sediments had been decreasing until 2010 followed by its increase in the open sea and in Taganrog Bay. The Cd content exceeded its clarke value throughout the study period. Cd elimination from the waters of the open sea was 0.9-6.0 tons/year, that from the waters of Taganrog Bay was 0.5-2.4 tons/year. These estimates of Cd fluxes into the bottom sediments can characterize sedimentation self-purification of waters. The period of sedimentation turnover of Cd in the open sea and Taganrog Bay at different Cd concentrations in water during the study period averaged 70 and 13.7 years, respectively, taking into account the differences in the volume of the studied water areas. Dependence of the coefficient of Cd accumulation by bottom sediments on its concentration in water showed that the increased intensity of sedimentation self-purification of waters at low Cd concentrations in water was provided by high concentrating ability of the bottom sediments associated with their granulometric composition. In the Sea of Azov, clay and silt sediments (fraction 0.01 mm) make up over 70%. With increasing degree of Cd contamination of waters, the accumulation coefficient value decreased and accordingly the contribution of sedimentation processes to water self-purification decreased. The assimilation capacity of the bottom sediments with respect to Cd amounted to 3.8 t/year in the open Sea of Azov and 0.7 t/year in Taganrog Bay.