Abstract Ammonium phospho-tellurate (PO4H2) 2PO4H(NH4)5Te(OH)6 a new ferroelectric recently discovered, has a phase transition at 48°C. We have applied cross polarization NMR between 1H and 31P and proton decoupling to measure the chemical shift tensors of the phosphorus in the two phase of the crystal. The 31 P chemical shift tensors obtained have been identified to their respective PO4 tetrahedra in the crystal. Their analysis and the study of their temperature dependence have enabled us to determine the nature of the order of the protons in the hydrogen bonds in the ferroelectric phase and the dynamic behaviour of the protons in the paraelectric phase and to understand the mechanism of the phase transition.