Epitaxial Pb(Zr0.35Ti0.65)O-3 (PZT) thin films with tetragonal symmetry and thicknesses ranging from 45 to 230 nm were grown at 540 A degrees C on SrRuO3-coated (001)SrTiO3 substrates by pulse-injected metalorganic chemical vapor deposition. The effect of the film thickness on the ferroelectric domain structure and the dielectric and ferroelectric properties were systematically investigated. Domain structure analysis of epitaxial PZT films was accomplished with high-resolution X-ray diffraction reciprocal space mapping and high-resolution transmission electron microscopy. Fully polar-axis (c-axis)-oriented epitaxial PZT thin films with high ferroelectric polarization values [e.g., remanent polarization (P (r)) similar to 90 mu C/cm(2)] were observed for film thicknesses below 70 nm. Films thicker than 70 nm had a c/a/c/a polydomain structure and the relative volume fraction of c-domains monotonously decreased to about 72% on increasing the film thickness up to 230 nm , and finally P (r) diminished to about 64 mu C/cm(2) for the 230-nm-thick epitaxial film. These polarization values were in good agreement with the estimated values taking into account the volume fraction of the c-axis-oriented domains while assuming a negligible contribution of 90A degrees domain reorientation caused by an externally applied electric field.