Abstract. Oxygen ion diffusion in oxides of the perovskite-type structure was determined by two methods of measurement: i) stepwise change of temperature or oxygen partial pressure of the gaseous environment of a ceramic sample, and measurement of the relaxation of electrical conductivity or oxygen content, ii) oxygen permeation through a gas dense oxide ceramic pellet from air to argon. The experimental problems and sources of errors, calculation methods of chemical diftusion coefficients and oxide ionic conductivities from these two modes of investigation are discussed. The comparison of relaxation and permeation measurements on 10 oxides of the type AI.~A'~M~_hM'~O3_o (A = La, Pr, Ce; A" = Sr, Ca; M = Mn, Fe; M" = Co, Ni) show advantages of the relaxation method in relation to the experimental performance and possible errors.