The ternary diagram of system Na2O-CdO-H2O at room temperature has been investigated. CdO and NaOH solids were used to prepare starting reactional systems. They were slowly hydrated by water vapor. Cadmium and sodium were analyzed in saturated solutions, at each step of the hydration process, using an ICP spectrometer. The solubility curves of gamma-Cd(OH), and Na2Cd(OH)(2) were drawn, and a value of the solubility product of gamma-Cd(OH), is proposed: K-sp = 4 X 10(-14) at room temperature.