The Differential Scanning Calorimetry DSC, Thermogravimetric Analysis TGA and Impedance Spectroscopy Technique were used in this work to study the behaviour of the KH 2 PO 4 with Fe 3 O 4 nanopowders, analyzing their phase behaviour in temperature ranges above room temperature up to 550 K. The KDP polycrystalline samples with Fe 2 O 3 nanopowders show three well defined endothermic peaks before their complete decomposition at higher temperatures, and the TGA results show a weight loss with increasing temperature, starting at the transition point of this peak. These results show a dehydration process before 475 K possibly due to structural changes in the samples.