The solubility in the Cd(HCOO)(2)-Sr(HCOO)(2)-H2O system has been studied by the method of physico-chemical analysis at 25 and 50 degrees C. It has been established that only simple salts crystallize in the system at 25 degrees C. A congruent double salt with composition CdSr(HCOO)(4).H2O is formed in the system at 50 degrees C. The thermal dehydration and decomposition of the new compound have been investigated by TG, DTA and DSC. The enthalpy of dehydration of CdSr(HCOO)(4).H2O has been determined.