CaCu3Ti4O12 (CCTO) ceramics with high dielectric constant (2-4 x 10(4)) and low loss (0.04) were prepared by the sol-gel process and sintered at 1050 degrees C for different times. The sintering time has a sensitive influence on the values of the dielectric constant and nonlinear coefficient. Tailored dielectric constant and nonlinear coefficient can be obtained by selecting a suitable sintering time according to different desired device application. The result of current-voltage characteristics and Cole-Cole plots in a broad temperature range (60-400 K) provide more effective evidence of the high dielectric constant supported by the grain boundary barrier layer (GBBL) capacitors model. Below 150 K, the GBBL capacitors effect weakens and gradually disappears with further decrease of temperature, thus leading the dielectric constant to decrease rapidly. Two values of grain activation energy acting at different temperature for each sample were obtained.