Impedance spectroscopy of the sintered Na2MnP2O7 ceramics was performed in the frequency range of 10 Hz – 3 GHz and 300-700 K temperature interval. Surprisingly, a significant decrease of conductivity was observed up to 340 K. It was shown, that a very small amount of water in the sodium-manganese-pyrophosphates effects their room temperature conductivity, which must be mixed Na+ and protonic at the same time. At 670-680 K a sharp increase of conductivity and dielectric permittivity was associated with a phase transition taking place in Na2MnP2O7. The anomalous change of electrical parameters at the phase transition temperature was frequency independent.