Ionic conduction, especially protonic conduction in pyrochlore-type structure oxide ceramics Ln(2)Zr(2-x)Y(x)O(7-alpha) (Ln = La, Nd, Gd and Sm) and Y(2)Ti(2-x)M(x)O(7-alpha) (M = In and Mg) was examined using electrochemical methods. Hydrogen concentration cells using Ln(2)Zr(2-x)Y(x)O(7-alpha) (Ln = La, Nd, Gd and Sm) ceramics as an electrolyte showed stable e.m.f., the values of which were close to the theoretical ones, indicating that the conduction was ionic. The conducting ions under this condition could be verified to be protons by electrochemical hydrogen permeation experiments. This showed mixed conduction of protons and electrons under water vapour concentration cell condition. Y(2)Ti(1.8)M(0.2)O(7-alpha) ceramics exhibited higher conductivity in hydrogen atmosphere than in air, but the hydrogen concentration cells using these ceramics as an electrolyte did not show any e.m.f., suggesting that they are not protonic conductors.