In various mixed ferrites, the relationship between disaccommodations (DA) and cation vacancy densities was investigated, the latter being estimated from the diffusion coefficients of isotopes. The relaxation time of DA–I observed at approximately 250°C was in agreement with an extrapolated value from the cation diffusion at elevated temperatures, and the two activation energies were nearly equal, 1.5 eV. The magnitude of DA–III observed at room temperature did not necessarily correspond to the vacancy density, i.e., an iron-poor Mn–Zn ferrite containing an appreciable amount of the vacancies did not exhibit DA–III.