Thermal decomposition of Zn(NO3)(2)(.)nH(2)O(n = 4 and 6) was studied using TG,DTA and QMS techniques. Measurements were performed in helium and in dry air. It was found that the examined reaction is a multi-step process with overlapping stages. The whole process depends on the rate of heating. Degradation of nitrate(V) groups starts before all water of crystallisation is removed from the system. Zn(NO3)(2)(.)2Zn(OH)(2) was identified as intermediate product of decomposition of Zn(NO3)(2)(.)nH(2)O. (C) 2003 Elsevier Science B.V. All rights reserved.