The ferroelectric properties and switching characteristics of rf sputtered PZT thin films were investigated as a function of film thickness (30–300 nm) and grain size. Electron microscopy was used to characterize the film microstructure. The film thickness was measured by ellipsometer. The results were analyzed for the individual contributions of film thickness and crystallite dimension to the size effects on the properties of ferroelectric thin films. A critical discussion of several different models describing the size effects was also presented.