Abstract. The structural correlations including the lattice constants and the mosaic dispersions between CeO2 and yttria-stabilized ZrO2 (YSZ) in CeO2/YSZ/Si(001) heteroepitaxial films have been investigated by out-of-plane and in-plane X-ray-diffraction techniques. The distinct linear correlations of the full width at half-maximum (FWHM) of the scan between CeO2 and YSZ have been found in both directions. CeO2 always has a 0.7 lower FWHM of the scan than YSZ in the out-of-plane direction, but has a 2.6 higher FWHM in the in-plane direction. A possible relationship between the out-of-plane and in-plane FWHMs of the scans has been demonstrated with a lattice-rotation model. Besides, the lattice constants of CeO2 are dependent on the FWHMs of the YSZ scans: as the FWHM is below 3.5, CeO2 has a tetragonal distortion, and as the FWHM is higher than 3.5, CeO2 exhibits a cubic structure without distortion. The results are of great interest, both for the fundamental understanding of the film-growth mechanisms and for potential applications.