We report on the effect of La0.5Sr0.5CoO3 (LSCO) bottom electrode to the dielectric properties of CaCu3Ti4O12 (CCTO) thin films grown on Ir/Ti/SiO2/Si substrates. Compared with the films grown directly on Ir/Ti/SiO2/Si substrates, the dielectric constant has been increased greatly about 100%, and the dielectric loss decreased to lower than 0.2 in the frequency range of 1-100 kHz. The origin has been discussed in details based on the analysis of the X-ray diffraction and impedance spectra measurements. Results of the impedance spectra suggest that the absence of undesired interfacial layer between Ir/CCTO thin films might be one of the major reasons of the improvement of the dielectric properties when the LSCO was introduced as the bottom electrode. (C) 2009 Elsevier B.V. All rights reserved.