Separation of cesium and cobalt from simulated medium active waste (MAW) by coprecipitation with hexacyanocobaltate (III) salts has been discussed. It has been found that coprecipitation of cesium or cobalt from MAW can be carried out successfully by using only potassium hexacyanocobaltate (III). The retention of cesium and cobalt has been studied over a wide range of pH, from zero to 12. A comparison of cobalti-, ferro- and ferricyanide complexes towards the retention of cesium at different pH values has also been made. The retention capacity of cobalticyanide precipitates for cesium and cobalt at pH 1.6 has been reported.