A new diammine zinc hydroxide nitrate, Zn5(OH)8(NO3)2.2NH3 and a new aquoammine zinc hydroxide nitrate, Zn5(OH)8(NO3)2.1.3NH3.0.7H2O, isostructural with Zn5(OH)8(NO3)2.2H2O, have been synthesized. It is demonstrated that the thermal decomposition process of these three compounds into ZnO, investigated by means of thermogravimetry, thermodiffractometry and mass spectrometry, depends upon the substitution rate of H2O by NH3 molecules. The diammine compound decomposes in two stages and the two others in three stages. A new ammine zinc hydroxide nitrate with the proposed chemicaL formuLa Zn(OH)(NO3).NH3 is formed in the first stage of the decomposition of the ammines. It has been characterized by its X-ray powder diffraction pattern. The formation of Zn3(OH)4(NO3)2 during the decompositions requires that the compounds are hydrated. However, the anhydrous solid Zn5(OH)8(NO3)2 is obtained only from the dihydrated hydroxysalt.