Ferroelectric Bi3.25La0.75Ti3O12 (BLT) thin films were fabricated by a metalorganic decomposition deposition aimed at investigating the thickness effect on ferroelectric properties. Both the grain growth behavior and ferroelectric properties (dielectric constant, remanent polarization) were found to be dependent on the thickness of the BLT thin films. We have found that an optimal film thickness occupies the range of 200–325 nm. The decrease in the film thickness below 200 nm causes a decrease in dielectric constant as well as in remanent polarization. The reasons are decreasing grain size and increasing internal strain probably resulted from the electrode/ferroelectric interfacial layer. The increase in the film thickness above 325 nm also leads to decreasing dielectric constant and remanent polarization, but also to increasing coercive field. This may be explained by a formation of interfacial layer with low dielectric constant as well as by the increase in internal strain as determined by x-ray diffraction analysis. © 2004 American Vacuum Society.