The new binary metal hydrogen phosphate monohydrate Mn05Ni0.5HPO4 center dot H2O was synthesized by a rapid and simple coprecipitation method using phosphoric acid, manganese metal, and nickel carbonate at ambient temperature. The kinetics of dehydration of Mn05Ni0.5HPO4 center dot H-20 was studied under nonisothermal heating by thermogravimetry (TG), and its final decomposition product was a binary metal pyrophosphate, MnNiP2O7. The activation energies of the dehydration step of Mn05Ni0.5HPO4 center dot H2O were calculated through the isoconversional methods of Ozawa and Kissinger-Akahira-Sunose (KAS), and the possible conversion functions have been estimated through the Coats-Redfern method. The activation energies calculated for the dehydration of Mn05Ni0.5HPO4 center dot H2O by different methods and techniques were found to be consistent. The possible conversion function of the dehydration reaction for Mn05Ni0.5HPO4 - H20 was "spherical symmetry" of a "three-dimensional diffusion mechanism".