PbZr0.5Ti0.5O3 thin films have been prepared on Pt (111)/Ti/SiO2/Si substrates by a modified sol-gel technique. The PZT films were annealed layer by layer using a rapid thermal annealing (RTA) method during the spin-coating process. A novel route was used to obtain PZT films with different single-annealed-layer in thickness from the same precursor solution. It is found that the degree of (111) orientation of the films increases with the reduction thickness of single-annealed-layer. As the thickness of single-annealed-layer drops to 40 nm, the film shows a high degree of (111) preferred orientation. The decrease of single-annealed-layer thickness also leads to the increase of the remanent polarization and the dielectric constant.