Thin CaCu33Ti44O1212 ceramic films have been successfully fabricated by a magnetron sputtering method and the surface morphology, microstructure and dielectric property of the samples have been measured by using atom force microscope, x-ray diffractometer (XRD) and LCR meter. XRD patterns show that the lattice constant of the films is less than that of the bulk materials, while the distort ion of the lattice in the films is comparatively larger. LCR results show that t he relative dielectric constant of the films is lower than that of the bulck mat erials at fixed temperature, and the temperature at which the dielectric constan t transits abruptly is higher and the activation energy of the films is larger. Further analysis shows that the lower crystallinity and more defects in the samp les result in the rapid decrease of the barrier layer capacity and film density, which should be responsible for the lower relative dielectric constant. The inc rease of the activation energy in the samples depends mainly on the factors such as internal stress, microstructure, defect and domain etc. The rapid increase o f the dielectric constant in lower frequency range implies that there exists int erface polarized phenomenon in the samples, which is related to the defects and dangling bonds on the interface.