The mixed compound NaH2(PO4)0.48(AsO4)0.52.H2O, which has been examined by Raman spectroscopy, XRD powder and dielectric, exhibits solid-solid phase transitions and one reversible solid-liquid phase transition. Besides, the investigation of dehydration behavior of sodium dihydrogenate phosphate-arsenate monohydrate was undertaken in the temperature range of 253 K to 333 K. The onset temperature of dehydration was determined from changes in ionic conductivity and X-ray powder on heating. It was confirmed by the Raman study not only in the disappearance of the vibrations assigned to the PO4, AsO4 stretching O***O bridge vibrations and the O***H-O vibrations, but also in the appearance of the new vibrations attributed to the (PO3), which constitutes the P-O-P chain, giving a polymer (with) the formula: NaH2(P2O7)x(As2O7)(1-x). The important variation was observed in all studies at 313 K whi ch co uld correspond to the transformation of the NDAP compounds of a solid crystal into a liquid form.