The microstructure, dielectric and electrical properties of CaCu3Ti4-xRxO12 (R=Y, Zr, Ta; x=0 and 0.005) ceramics were investigated by XRD, Raman spectra, SEM and dielectric spectrum measurements. Positron annihilation measurements have been performed to investigate the influence of doping on the defects. The results show that all samples form a single crystalline.phase. Yand Ta doping cause different defect types and increase the defect size and concentration, which influence the mobility of grain boundary and result in the different grain size. Y doping increases the dielectric constant and decreases the nonlinear property while Ta doping lead to an inverse result. Zr-doped sample has'nearly the defect type, grain morphology and dielectric properties as pure CaCu3Ti4O12. The effects of microstructure including the grain morphology and the vacancy defects on the mechanism of the dielectric and electric properties by doping are discussed. (C) 2015 Elsevier Ltd. All rights reserved.