Yttria-stabilized zirconia (YSZ) ceramic is considered as an attractive matrix for nuclear applications, such as inert matrix for the destruction of excess plutonium or good host material for nuclear waste storage. Some actinide elements in high-level radioactive wastes can be simulated by cerium as tetravalent actinide, and gadolinium as trivalent actinide or neutron absorber. The present work is focused on the diffusion study of Ce and Gd in YSZ single crystal and high density polycrystals. A thin film of Ce or Gd was deposited either by spin-coating method or by physical vapour deposition on the surface of polished samples. The diffusion experiments were performed from 1173 to 1673 K under air. The Ce or Gd diffusion profiles were determined by secondary ion mass spectrometry. The experiments led to the determination of effective diffusion coefficient, Deff, bulk and grain boundary diffusion coefficients, DB and DGB. The dependence of these diffusion coefficients on temperature is described by means of Arrhenius equations and the diffusivity is compared with literature.