Retention loss is a significant issue for an application of ferroelectric thin films to high-density non-volatile memory devices. We investigated the polarization retention characteristics of ferroelectric Pb(Zr,Ti)O3 (PZT) thin films which were fabricated on Pt/IrO2/Ir substrates by different deposition methods. In thermally-accelerated retention failure tests, Pb(Zr,Ti)O3 (PZT) films which were prepared by a chmeical solution deposition (CSD) method showed rapid decay of retained polarization charges as the films became thinner down to 1000 Å, while the films which were grown by metal organic chemical vapor deposition (MOCVD) showed relatively large nonvolatile charges at the same thickness. We concluded that in the CSD-grown films, the relatively large interfacial passive layer compared with the MOCVD-grown films had an unfavorable effect on retention behavior. We observed the existence of such interfacial layers by extrapolation of the total capacitance with thickness of the films and the capacitance of this layer was larger in MOCVD-grown films. It means that the possibility of the accumulation of space charges at the interface was reduced, so that less imprint and less retention loss could be observed in the MOCVD-grown films.