PLZT (8/67/33) thin films were deposited on both Pt/SiO2/Si rind Pt/Ti/SiO2/Si substrates by electron cyclotron resonance chemical vapor deposition for various deposition times. The nucleation growth mechanism, and the thickness dependence of the dielectric constant of PLZT films on the substrate were investigated. At the initial stage of PLZT film deposition, the incorporation of Pb into the film is very difficult because of the high volatility of Pb oxide molecules on the Pt substrate, resulting in the formation of a Pb-deficient interfacial layer. The degree of Pb deficiency at the interface is more severe on the Pt/SiO2/Si substrate. For the Pt/SiO2/Si substrate, a very thick Pb-deficient interfacial layer forms and the non-perovskite phase becomes dominant. For the Pt/Ti/SiO2/Si substrate, Ti atoms which out-diffused to the substrate surface through the gain boundaries of the Pt layer facilitate the incorporation of Pb. which leads to the nucleation of a perovskite phase at the substrate grain boundaries and promotes the growth of the perovskite phase. The dielectric constant of the bulk PLZT film is 1420. However, the dielectric constant of the film decreases with decreasing film thickness due to the existence of the low dielectric interfacial layer.