The conductivity of a mesoporous zirconium phosphate pyrophosphate of composition Zr(P2O7)(0.81)(O3POH)(0.38) and surface area of 215 m(2)/g has been determined as a function of temperature at controlled relative humidity. Ac and de conductivity measurements carried out on pellets with platinum electrodes, in nitrogen or hydrogen flow, showed that the charge carriers are protons. At 20 degrees C and relative humidity decreasing in the range 90-20%, the conductivity changes from 1.3 x 10(-3) S cm(-1) to 4 x 10(-7) S cm(-1). The activation energy for conduction in the range 20/ - 20 degrees C increases from 4.6 to 8.7 kcal/mol with decreasing relative humidity. At 100 degrees C and 90% relative humidity the pyrophosphate groups undergo a slow rehydration and the conductivity rises up to 2.6 x 10(-3) S cm(-1) as a consequence of the increase of the number of -POH groups.