The high dielectric constant presented by CaCu3Ti4O12 (CCTO) makes this material promising for industrial applications, in particular for electronic devices. Nevertheless, the preparation method and the doping by oxides has a great influence on the microstructure, and consequently in the dielectric properties. In this work we prepared and studied CCTO doped by germanium oxide, in concentrations up to 10% by weight. X-ray diffraction shows the presence of nanocristals. The grains and the grain boundaries compositions have been characterized by scanning electron microscopy with energy dispersive X-ray spectrometry mapping. The magnetization measurements show an antiferromagnetic behaviour with a Néel temperature TN=25 K, independent of the GeO2 doping (up to 6%). Analyses of the high temperature dependence of the magnetic susceptibility show that the increase of the GeO2 doping decreases the paramagnetic temperature. Dielectric spectroscopy measurements, in the frequency range from 75 kHz to 30 MHz, at room temperature, have been carried out. Cole-Cole model of dielectric relaxation adjusts correctly the data. The results, obtained with the different techniques, indicate that there is the increase of samples grain size up to 6% of germanium oxide, which causes an increase of the real and imaginary parts of complex permittivity.